EN-304-617.md.backup

- Merkle Trees: https://en.wikipedia.org/wiki/Merkle_tree
- Digital Signatures: https://csrc.nist.gov/projects/digital-signatures
- Tamper-Evident Storage: https://csrc.nist.gov/glossary/term/tamper_evident

## 6.5 Update Mechanism Security Assessments

This section covers assessment procedures for requirements UPD-REQ-1 through UPD-REQ-23, addressing secure update delivery, signature verification, rollback protection, update channels, and update transparency.

### Assessment: UPD-REQ-1 (Automatic update mechanism)

**Reference**: UPD-REQ-1 - Browser shall implement an automatic update mechanism that checks for and applies security updates without user intervention

**Given**: A conformant browser with UPD-1 or higher capability

**Task**: Verify that automatic updates prevent users from running vulnerable browser versions by ensuring security patches are promptly applied without requiring user awareness or action. Manual update processes fail because users often ignore update notifications or delay patching, leaving exploitable vulnerabilities active for extended periods. Automatic updates close this security gap by applying critical fixes as soon as they become available.

**Verification**:

1. Install the browser and configure it to allow automatic updates (verify this is the default setting)
2. Check the browser's update settings to confirm automatic updates are enabled
3. Access the browser's internal update interface through the settings menu
4. Monitor the browser's update check schedule by reviewing internal logs or using network monitoring tools
5. Simulate an available update by configuring a test update server or using the browser's internal testing mechanisms
6. Verify that the browser automatically checks for updates at the configured interval (typically daily)
7. Confirm that updates are downloaded in the background without blocking browser operation
8. Verify that updates are applied either at browser restart or in the background without user intervention
9. Test that the browser prompts for restart only when necessary for update installation
10. Verify that the automatic update mechanism continues to function across browser restarts and system reboots
11. Automatic update checks occur at regular intervals without user action
12. Updates are downloaded in the background without interrupting browsing
13. Update installation is automated with minimal or no user interaction required
14. Browser update status is clearly displayed to the user
15. Update checks occur even when the browser is running in background mode
16. Failed update attempts are retried automatically

**Pass Criteria**: Browser automatically checks for updates at least daily AND downloads and applies updates without mandatory user intervention AND update status is visible to users

**Fail Criteria**: Automatic updates require manual user action to initiate OR updates fail to check automatically OR update mechanism can be permanently disabled by users

**Evidence**: Screenshots of automatic update settings and status pages, network packet captures showing update check requests, browser internal logs showing update schedule, time-stamped video of automatic update process, configuration file exports showing update settings

**References**:

- Chrome Update Architecture: https://chromium.googlesource.com/chromium/src/+/main/docs/updater/functional_spec.md
- Firefox Update System: https://wiki.mozilla.org/Software_Update
- Microsoft Edge Update Policies: https://docs.microsoft.com/en-us/deployedge/microsoft-edge-update-policies
- NIST SP 800-40 Guide to Enterprise Patch Management: https://csrc.nist.gov/publications/detail/sp/800-40/rev-4/final
- CIS Browser Security Benchmarks: https://www.cisecurity.org/benchmark/google_chrome

### Assessment: UPD-REQ-2 (Update signature verification)

**Reference**: UPD-REQ-2 - Browser shall verify cryptographic signatures of all updates before installation using trusted public keys

**Given**: A conformant browser with UPD-1 or higher capability

**Task**: Verify that update signature verification prevents distribution of malicious browser versions by ensuring only authentic vendor-signed packages can be installed, even if update infrastructure is compromised or man-in-the-middle attacks occur. Without cryptographic signature verification, attackers who compromise update servers or intercept update traffic can inject backdoored browser binaries, resulting in complete system compromise for all affected users.

**Verification**:

1. Obtain a legitimate browser update package from the official distribution channel
2. Extract the update package and locate the cryptographic signature file or embedded signature
3. Verify the signature algorithm used (should be RSA-4096, ECDSA-P384, or stronger)
4. Attempt to modify the update package contents and observe that signature verification fails
5. Create a test update package signed with an untrusted key and attempt to install it
6. Monitor the browser's update process using system call tracing tools to verify signature verification occurs
7. Check that the browser's trusted public keys are embedded in the binary or stored in a protected location
8. Verify that signature verification failures prevent update installation and generate error logs
9. Test that the browser rejects updates with missing signatures
10. Confirm that signature verification occurs before any update content is executed
11. All update packages include valid cryptographic signatures
12. Signature verification uses strong cryptographic algorithms (RSA-4096, ECDSA-P384, or better)
13. Modified update packages are rejected due to signature verification failure
14. Updates signed with untrusted keys are rejected
15. Signature verification occurs before any update code execution
16. Verification failures are logged and reported to the user
17. Trusted public keys are protected from tampering

**Pass Criteria**: All updates are cryptographically signed AND signatures are verified before installation AND modified or incorrectly signed updates are rejected

**Fail Criteria**: Updates can be installed without valid signatures OR signature verification can be bypassed OR weak cryptographic algorithms are used (RSA-2048 or weaker)

**Evidence**: Update package signature files, signature verification logs, network traces of update downloads showing signature transmission, system call traces showing verification process, test results from modified update packages, cryptographic algorithm analysis

**References**:

- Mozilla Code Signing Policy: https://wiki.mozilla.org/Security/Binary_Transparency
- NIST FIPS 186-5 Digital Signature Standard: https://csrc.nist.gov/publications/detail/fips/186/5/final
- Authenticode Code Signing (Windows): https://docs.microsoft.com/en-us/windows-hardware/drivers/install/authenticode
- Apple Code Signing Guide: https://developer.apple.com/library/archive/documentation/Security/Conceptual/CodeSigningGuide/
- OWASP Code Signing Best Practices: https://cheatsheetseries.owasp.org/cheatsheets/Third_Party_Javascript_Management_Cheat_Sheet.html

### Assessment: UPD-REQ-3 (HTTPS-only update delivery)

**Reference**: UPD-REQ-3 - Browser shall download all updates exclusively over HTTPS with certificate validation and pinning

**Given**: A conformant browser with UPD-1 or higher capability

**Task**: Verify that HTTPS-only update delivery protects update packages from interception and modification during transit, preventing network attackers from injecting malicious code even before signature verification. While signature verification provides end-to-end authenticity, transport encryption prevents metadata leakage about which browser versions are vulnerable and adds defense-in-depth against implementation flaws in signature verification.

**Verification**:

1. Configure a network proxy to intercept browser update traffic
2. Monitor network traffic during an update check to verify all connections use HTTPS
3. Attempt to redirect update requests to HTTP endpoints using DNS spoofing or proxy manipulation
4. Verify that the browser rejects HTTP update URLs and only accepts HTTPS
5. Test certificate validation by presenting an invalid certificate for the update server
6. Check if the browser implements certificate pinning for update domains
7. Attempt a man-in-the-middle attack on the update channel using a rogue certificate
8. Verify that TLS 1.2 or higher is used for all update connections
9. Test that the browser verifies the update server's hostname matches the certificate
10. Confirm that update requests include proper TLS configurations (strong cipher suites, no deprecated protocols)
11. All update downloads occur exclusively over HTTPS connections
12. HTTP update URLs are rejected or automatically upgraded to HTTPS
13. TLS 1.2 or TLS 1.3 is enforced for all update traffic
14. Certificate validation is performed with proper hostname verification
15. Certificate pinning is implemented for update domains
16. Man-in-the-middle attacks on update channels are detected and blocked
- Strong cipher suites are negotiated (AES-GCM, ChaCha20-Poly1305)
- Deprecated protocols (TLS 1.0, TLS 1.1, SSLv3) are rejected

**Pass Criteria**: All update traffic uses HTTPS with TLS 1.2+ AND certificate validation is enforced AND HTTP update URLs are rejected AND certificate pinning is implemented for critical update domains

**Fail Criteria**: Updates can be downloaded over HTTP OR TLS 1.1 or earlier is accepted OR certificate validation can be bypassed OR no certificate pinning is implemented

**Evidence**: Network packet captures showing HTTPS-only update traffic, TLS handshake analysis, certificate chain validation logs, test results from HTTP redirect attempts, man-in-the-middle attack test results, cipher suite negotiation logs

**References**:

- Chrome Update Server Pinning: https://www.chromium.org/Home/chromium-security/security-faq/#TOC-How-does-key-pinning-work-in-Chrome-
- Mozilla Update Server Security: https://wiki.mozilla.org/Security/Server_Side_TLS
- NIST SP 800-52 TLS Guidelines: https://csrc.nist.gov/publications/detail/sp/800-52/rev-2/final
- IETF RFC 8446 TLS 1.3: https://www.rfc-editor.org/rfc/rfc8446
- OWASP Transport Layer Security: https://cheatsheetseries.owasp.org/cheatsheets/Transport_Layer_Security_Cheat_Sheet.html
- Certificate Pinning Best Practices: https://owasp.org/www-community/controls/Certificate_and_Public_Key_Pinning

### Assessment: UPD-REQ-4 (Update manifest integrity)

**Reference**: UPD-REQ-4 - Browser shall verify the integrity of update manifests containing version information, file hashes, and metadata

**Given**: A conformant browser with UPD-1 or higher capability

**Task**: Verify that update manifest integrity protects the update metadata from tampering, ensuring that version information, file hashes, and download URLs cannot be manipulated by attackers to redirect updates to malicious files or bypass security checks. Compromised manifests can trick browsers into downloading wrong versions or accepting manipulated update files even when signature verification is implemented.

**Verification**:

1. Capture an update manifest file during a browser update check (typically JSON or XML format)
2. Examine the manifest structure to verify it includes: version number, file hashes, file sizes, signature, and metadata
3. Verify that the manifest itself is signed and the signature is validated before processing
4. Attempt to modify the manifest file (change version number or file hashes) and verify it is rejected
5. Test that each file listed in the manifest includes a cryptographic hash (SHA-256 or stronger)
6. Verify that downloaded update files are checked against the manifest hashes before installation
7. Test that mismatched file hashes prevent installation and trigger error handling
8. Check that the manifest includes timestamp information to prevent replay attacks
9. Verify that the manifest specifies minimum supported versions for rollback protection
10. Confirm that manifest validation failures are logged and prevent update installation
11. Update manifests are cryptographically signed and signatures are verified
12. Manifests include complete metadata: version, file hashes (SHA-256+), sizes, timestamps
13. Modified manifests are rejected due to signature verification failures
14. Each update file is verified against manifest hashes before installation
15. Hash mismatches prevent installation and generate error logs
16. Manifests include rollback protection information (minimum version)
17. Timestamp validation prevents replay attacks
18. Manifest structure follows a well-defined schema

**Pass Criteria**: Update manifests are signed and verified AND contain file hashes (SHA-256+) for all components AND hash verification is enforced before installation AND manifest tampering is detected and rejected

**Fail Criteria**: Manifests are not signed OR file hashes are missing or not verified OR modified manifests are accepted OR weak hash algorithms (MD5, SHA-1) are used

**Evidence**: Update manifest files in JSON/XML format, manifest signature verification logs, test results from modified manifests, hash verification logs, network captures showing manifest downloads, schema validation results

**References**:

- Chrome Update Manifest Format: https://chromium.googlesource.com/chromium/src/+/main/docs/updater/protocol_3_1.md
- The Update Framework (TUF) Specification: https://theupdateframework.github.io/specification/latest/
- NIST SP 800-107 Hash Function Recommendations: https://csrc.nist.gov/publications/detail/sp/800-107/rev-1/final
- Google Omaha Protocol: https://github.com/google/omaha/blob/main/doc/ServerProtocolV3.md
- OWASP Software Supply Chain Security: https://owasp.org/www-project-software-component-verification-standard/

### Assessment: UPD-REQ-5 (Rollback protection)

**Reference**: UPD-REQ-5 - Browser shall implement rollback protection to prevent installation of older versions with known vulnerabilities

**Given**: A conformant browser with UPD-1 or higher capability

**Task**: Verify that rollback protection prevents attackers from downgrading browsers to older versions containing known exploitable vulnerabilities, blocking a common attack vector where adversaries force installation of vulnerable software to exploit publicly disclosed flaws. Without rollback protection, attackers who compromise update infrastructure or perform man-in-the-middle attacks can systematically downgrade browser installations to versions with known, weaponized exploits.

**Verification**:

1. Identify the currently installed browser version number
2. Obtain an older version of the browser update package (at least 2-3 versions older)
3. Attempt to install the older update package through the automatic update mechanism
4. Verify that the browser rejects the installation with an appropriate error message
5. Check the browser's update configuration for minimum version enforcement policies
6. Test that the browser maintains a record of the highest version ever installed
7. Attempt to manually downgrade the browser by installing an older version package
8. Verify that critical security updates cannot be rolled back even by administrators
9. Test that the rollback protection persists across browser reinstallations (if applicable)
10. Confirm that rollback protection errors are logged with version information
11. Browser rejects installation of older versions through automatic update mechanism
12. Minimum version numbers are enforced based on security requirements
13. Manual downgrade attempts are blocked or generate security warnings
14. Browser maintains persistent version history to detect rollback attempts
15. Critical security milestone versions cannot be downgraded
16. Rollback protection applies to both full updates and component updates
17. Clear error messages indicate rollback protection enforcement
18. Version comparison logic handles all version number formats correctly

**Pass Criteria**: Browser prevents installation of older versions through automatic updates AND maintains version history to detect rollbacks AND critical security versions cannot be downgraded

**Fail Criteria**: Older versions can be installed through update mechanism OR no minimum version enforcement exists OR rollback protection can be easily bypassed

**Evidence**: Update rejection logs showing version mismatch errors, test results from downgrade attempts, version history configuration files, error messages from rollback protection, policy configuration showing minimum version requirements

**References**:

- Chrome Version Enforcement: https://chromeenterprise.google/policies/#TargetVersionPrefix
- Android Rollback Protection: https://source.android.com/docs/security/features/verifiedboot/verified-boot#rollback-protection
- TUF Rollback Attack Prevention: https://theupdateframework.io/docs/security/
- NIST Cybersecurity Framework - Update Management: https://www.nist.gov/cyberframework
- Mozilla Update Security Guidelines: https://wiki.mozilla.org/Security/Server_Side_TLS
- Microsoft Update Rollback Protection: https://docs.microsoft.com/en-us/windows/deployment/update/waas-restart

### Assessment: UPD-REQ-6 (Update channel isolation)

**Reference**: UPD-REQ-6 - Browser shall maintain isolation between update channels (stable, beta, dev) with independent signature verification

**Given**: A conformant browser with UPD-1 or higher capability supporting multiple channels

**Task**: Verify that update channel isolation prevents attackers from injecting unstable or experimental browser versions into production deployments by ensuring strict separation between stable, beta, and development update streams. Without channel isolation, compromised development infrastructure or testing servers could be leveraged to push untested code to stable channel users, introducing vulnerabilities or instability into production environments.

**Verification**:

1. Identify the available update channels for the browser (stable, beta, dev, canary)
2. Install the browser in stable channel mode and verify the update channel configuration
3. Examine the update server URLs for each channel to verify they are distinct
4. Attempt to inject a beta or dev channel update into a stable channel installation
5. Verify that each channel uses separate signature verification keys or key policies
6. Test that switching between channels requires explicit user action and confirmation
7. Check that channel metadata is included in update manifests and verified
8. Attempt to downgrade from stable to beta channel and verify the security implications are communicated
9. Verify that each channel has independent version numbering and rollback protection
10. Confirm that cross-channel update injection attempts are logged and rejected
11. Each update channel has distinct update server endpoints
12. Channel-specific signature verification prevents cross-channel update injection
13. Update manifests include channel identification that is verified
14. Channel switching requires explicit user consent and configuration changes
15. Downgrading channels (stable to beta/dev) triggers security warnings
16. Channel isolation prevents malicious update server redirection
17. Each channel maintains independent version history and rollback protection
18. Cross-channel update attempts are detected and logged

**Pass Criteria**: Update channels use separate server endpoints AND channel-specific signature verification prevents injection AND channel switching requires explicit user action AND cross-channel updates are rejected

**Fail Criteria**: Update channels share signature keys OR cross-channel updates can be injected OR no channel verification in update manifests OR channel switching occurs without user consent

**Evidence**: Update server URL configurations for each channel, signature verification key policies, channel metadata in update manifests, test results from cross-channel injection attempts, channel switching logs, network traces showing channel-specific endpoints

**References**:

- Chrome Release Channels: https://www.chromium.org/getting-involved/dev-channel/
- Firefox Release Management: https://wiki.mozilla.org/Release_Management/Release_Process
- Microsoft Edge Channels: https://docs.microsoft.com/en-us/deployedge/microsoft-edge-channels
- Google Chrome Enterprise Channel Management: https://support.google.com/chrome/a/answer/9982578
- NIST Secure Software Development Framework: https://csrc.nist.gov/Projects/ssdf

### Assessment: UPD-REQ-7 (Component update support)

**Reference**: UPD-REQ-7 - Browser shall support independent security updates for components (rendering engine, JavaScript engine, libraries) without full browser updates

**Given**: A conformant browser with UPD-2 or higher capability

**Task**: Verify that component-level updates enable rapid patching of critical subsystems like JavaScript engines or rendering engines without waiting for full browser release cycles, reducing the window of exposure for component-specific vulnerabilities. Monolithic update systems delay security fixes because all components should be tested together, while independent component updates allow targeted, accelerated security patching for high-risk subsystems.

**Verification**:

1. Identify the browser's major components that support independent updates (e.g., V8, Chromium base, libraries)
2. Monitor the update mechanism to detect component-specific update packages
3. Verify that component updates include version information and dependency specifications
4. Test that component updates are applied without requiring a full browser restart when possible
5. Attempt to install incompatible component versions and verify dependency checking prevents installation
6. Check that component updates follow the same security verification as full updates (signatures, HTTPS)
7. Verify that component update manifests specify compatibility with browser versions
8. Test that critical component vulnerabilities can be patched independently of the full release schedule
9. Confirm that component updates maintain rollback protection independently
10. Verify that component update status is visible in the browser's update interface
11. Individual components can be updated independently of full browser updates
12. Component updates include version and dependency metadata
13. Component updates are signed and verified like full browser updates
14. Incompatible component versions are rejected based on dependency checking
15. Component updates can be applied with minimal or no browser restart
16. Critical security components can be updated on accelerated schedules
17. Component update history is tracked separately from full browser versions
18. Update interface displays component-level version information

**Pass Criteria**: Browser supports independent component updates with signature verification AND dependency checking prevents incompatible installations AND component updates follow same security verification as full updates

**Fail Criteria**: No support for component-level updates OR component updates bypass security verification OR no dependency checking for component compatibility

**Evidence**: Component update manifest files, component version listings from browser internals, update logs showing component-specific updates, dependency verification results, signature verification for component updates, test results from incompatible component installations

**References**:

- Chrome Component Updates: https://chromium.googlesource.com/chromium/src/+/main/components/component_updater/README.md
- V8 Engine Versioning: https://v8.dev/docs/version-numbers
- WebRTC Component Updates: https://webrtc.github.io/webrtc-org/release-notes/
- NIST Software Component Verification: https://csrc.nist.gov/Projects/cyber-supply-chain-risk-management
- OWASP Dependency Check: https://owasp.org/www-project-dependency-check/

### Assessment: UPD-REQ-8 (Emergency update capability)

**Reference**: UPD-REQ-8 - Browser shall support emergency update mechanism for critical zero-day vulnerabilities with accelerated deployment

**Given**: A conformant browser with UPD-1 or higher capability

**Task**: Verify that emergency update mechanisms enable rapid deployment of critical zero-day patches to all users before exploit code becomes widely available, minimizing the window of vulnerability exploitation. Standard rollout schedules of days or weeks are unacceptable for actively exploited vulnerabilities, requiring accelerated deployment paths that bypass normal staged rollouts while maintaining security verification integrity.

**Verification**:

1. Review the browser's update documentation for emergency or critical update procedures
2. Examine update check frequency configuration and verify it can be increased for critical updates
3. Test that the browser can be configured to prioritize critical security updates over feature updates
4. Simulate an emergency update scenario by configuring a test update with high-priority flags
5. Verify that emergency updates bypass normal staged rollout delays
6. Test that users receive prominent notifications for critical security updates requiring immediate action
7. Check that emergency updates can trigger forced restarts with appropriate user warnings
8. Verify that emergency update flags cannot be spoofed by malicious update servers
9. Test that emergency updates are logged with high-priority markers for audit purposes
10. Confirm that emergency update mechanisms include additional verification to prevent abuse
11. Browser supports accelerated update checks for critical security updates
12. Emergency updates include priority flags in update manifests
13. Critical updates bypass staged rollout mechanisms for faster deployment
14. Users receive prominent notifications for emergency security updates
15. Emergency updates can trigger forced restarts with clear security justification
16. Emergency update flags are authenticated and cannot be spoofed
17. Audit logs distinguish emergency updates from regular updates
18. Emergency update mechanism includes safeguards against abuse

**Pass Criteria**: Browser supports emergency update mechanism with accelerated deployment AND emergency updates bypass normal rollout delays AND priority flags are authenticated AND users are clearly notified of critical updates

**Fail Criteria**: No emergency update mechanism exists OR emergency updates follow normal rollout schedule OR priority flags can be spoofed OR users cannot distinguish critical from regular updates

**Evidence**: Emergency update configuration documentation, test results from simulated critical updates, update priority flags in manifests, notification screenshots for critical updates, audit logs showing emergency update markers, rollout bypass verification

**References**:

- Chrome Critical Update Deployment: https://chromereleases.googleblog.com/
- Firefox Critical Updates: https://www.mozilla.org/en-US/security/advisories/
- NIST SP 800-40 Emergency Patching: https://csrc.nist.gov/publications/detail/sp/800-40/rev-4/final
- CERT Vulnerability Disclosure: https://vuls.cert.org/confluence/display/Wiki/Vulnerability+Disclosure+Policy
- Microsoft Security Response Center: https://www.microsoft.com/en-us/msrc

### Assessment: UPD-REQ-9 (Update verification before installation)

**Reference**: UPD-REQ-9 - Browser shall perform complete integrity verification of all update files before beginning installation process

**Given**: A conformant browser with UPD-1 or higher capability

**Task**: Verify that update verification prevents installation of compromised or tampered browser builds, ensuring only authentic vendor-signed updates can be applied even if the update server or distribution network is compromised. This prevents attackers from injecting malicious code through man-in-the-middle attacks, compromised CDNs, or corrupted downloads that bypass cryptographic verification.

**Verification**:

1. Monitor the browser update process to identify the verification phase before installation
2. Capture update files during download and verify that hashes match the update manifest
3. Corrupt an update file after download but before installation to test verification
4. Verify that corrupted files are detected and re-downloaded before installation proceeds
5. Test that partial downloads are detected and not installed
6. Check that all update files are verified against the signed manifest before any installation steps
7. Verify that installation only begins after all files pass integrity checks
8. Test that verification failures trigger error handling and logging
9. Confirm that failed verifications do not leave the browser in an unstable state
10. Verify that the verification process cannot be bypassed or interrupted
11. All update files are verified against cryptographic hashes before installation
12. Hash algorithms used are SHA-256 or stronger
13. Corrupted or modified files are detected and rejected
14. Partial downloads are detected and completed before installation
15. Installation begins only after complete verification of all update components
16. Verification failures trigger automatic re-download or error reporting
17. Failed verifications are logged with specific error information
18. Browser remains in stable state if verification fails

**Pass Criteria**: All update files are verified with cryptographic hashes (SHA-256+) before installation AND corrupted files are detected and re-downloaded AND installation only proceeds after complete verification

**Fail Criteria**: Update files are installed without verification OR weak hash algorithms are used OR corrupted files can be installed OR verification can be bypassed

**Evidence**: Update verification logs showing hash checks, test results from corrupted file installations, network traces showing re-download behavior, hash algorithm analysis, installation process flow documentation, error handling logs

**References**:

- Chrome Update Verification: https://chromium.googlesource.com/chromium/src/+/main/docs/updater/functional_spec.md#verification
- Mozilla Update Integrity Checks: https://wiki.mozilla.org/Software_Update#Integrity_Checks
- NIST Hash Function Security: https://csrc.nist.gov/projects/hash-functions
- TUF Consistent Snapshot Protection: https://theupdateframework.github.io/specification/latest/#consistent-snapshots
- ISO/IEC 29147 Vulnerability Disclosure: https://www.iso.org/standard/72311.html

### Assessment: UPD-REQ-10 (Update failure recovery)

**Reference**: UPD-REQ-10 - Browser shall implement robust failure recovery mechanisms to restore functionality if update installation fails

**Given**: A conformant browser with UPD-1 or higher capability

**Task**: Verify that update failure recovery mechanisms maintain browser availability and security posture even when updates fail, preventing denial-of-service scenarios where failed updates render the browser unusable or leave it in a vulnerable state. This ensures users retain access to a functional, secure browser and prevents attackers from exploiting update failures to create persistent availability issues.

**Verification**:

1. Create a test scenario where update installation fails (disk full, permission denied, file corruption)
2. Trigger an update and simulate installation failure at various stages (download, verification, installation)
3. Verify that the browser rolls back to the previous working version after installation failure
4. Test that the browser remains functional and can be launched after a failed update
5. Verify that failed update state is detected and reported to the user with clear messaging
6. Test that the browser automatically retries failed updates with exponential backoff
7. Simulate power loss or system crash during update installation
8. Verify that the browser can recover from interrupted updates on next launch
9. Test that update failure recovery preserves user data and settings
10. Confirm that recovery processes are logged for troubleshooting
11. Failed updates do not prevent browser from launching or functioning
12. Browser automatically rolls back to previous version after installation failures
13. User data and settings are preserved through failed update attempts
14. Clear error messages indicate update failure causes
15. Automatic retry mechanisms with exponential backoff are implemented
16. Interrupted updates (power loss, crash) are detected and recovered on next launch
17. Recovery processes maintain browser stability and security
18. All recovery actions are logged with timestamps and error codes

**Pass Criteria**: Browser remains functional after update failures AND automatically rolls back to working version AND retries failed updates automatically AND preserves user data through failures

**Fail Criteria**: Failed updates prevent browser launch OR no rollback mechanism exists OR user data is corrupted by failed updates OR no automatic retry for failed updates

**Evidence**: Update failure logs with error codes, rollback process documentation, test results from simulated failures (disk full, crash, corruption), user data integrity verification, retry attempt logs with backoff timing, recovery process screenshots

**References**:

- Chrome Update Recovery: https://chromium.googlesource.com/chromium/src/+/main/docs/updater/functional_spec.md#error-handling
- NIST Resilience Engineering: https://csrc.nist.gov/glossary/term/resilience
- Google Omaha Error Handling: https://github.com/google/omaha/blob/main/doc/ServerProtocolV3.md#error-codes

### Assessment: UPD-REQ-11 (Update transparency logging)

**Reference**: UPD-REQ-11 - Browser shall implement update transparency logging to create auditable records of all update activities

**Given**: A conformant browser with UPD-1 or higher capability and LOG-1 or higher capability

**Task**: Verify that update transparency logging creates auditable records of all update activities, enabling detection of compromised update infrastructure, supply chain attacks, or unauthorized modifications to the browser. This provides forensic evidence for security incident investigation and enables organizations to verify that only legitimate, authorized updates were applied to their browser fleet.

**Verification**:

1. Enable update logging through browser configuration or developer tools
2. Perform a complete update cycle and capture all generated logs
3. Verify that logs include: update check timestamps, available versions, download start/completion, verification results, installation status
4. Test that update logs include cryptographic hashes of installed components
5. Verify that signature verification results are logged with key identifiers
6. Check that update server URLs and responses are logged for audit purposes
7. Test that all update failures are logged with specific error codes and context
8. Verify that logs include user actions related to updates (manual checks, deferrals, channel changes)
9. Confirm that update logs can be exported for external analysis or compliance reporting
10. Test that update logs are protected from tampering and include integrity verification
11. All update activities are logged with timestamps and version information
12. Logs include download sources, file hashes, and signature verification results
13. Update failures are logged with detailed error information
14. User actions related to updates are captured in logs
15. Logs are structured and machine-readable (JSON or similar format)
16. Update logs can be exported for compliance and audit purposes
17. Logs include sufficient detail for security incident investigation
18. Log integrity is protected through checksums or signing

**Pass Criteria**: All update activities are logged with complete details AND logs include hashes and verification results AND logs are exportable in structured format AND log integrity is protected

**Fail Criteria**: Update activities are not logged OR logs lack critical information (timestamps, versions, hashes) OR logs cannot be exported OR logs can be tampered with

**Evidence**: Complete update log files showing full update cycle, exported logs in JSON/structured format, log integrity verification results, test results showing failure logging, screenshots of update log interfaces, compliance report samples

**References**:

- Chrome Update Logging: https://chromium.googlesource.com/chromium/src/+/main/docs/updater/functional_spec.md#logging
- Binary Transparency: https://wiki.mozilla.org/Security/Binary_Transparency
- NIST SP 800-92 Log Management: https://csrc.nist.gov/publications/detail/sp/800-92/final
- Google Binary Authorization: https://cloud.google.com/binary-authorization/docs
- Certificate Transparency RFC 6962: https://www.rfc-editor.org/rfc/rfc6962
- OWASP Logging Cheat Sheet: https://cheatsheetseries.owasp.org/cheatsheets/Logging_Cheat_Sheet.html

### Assessment: UPD-REQ-12 (Delta update security)

**Reference**: UPD-REQ-12 - Browser shall securely implement delta updates (patches) with same security verification as full updates

**Given**: A conformant browser with UPD-2 or higher capability supporting delta updates

**Task**: Verify that delta update security prevents attackers from exploiting differential patching mechanisms to inject malicious code through crafted patch files that bypass full binary verification. Delta updates introduce unique attack vectors where malicious patches could transform a legitimate binary into a compromised one if the patch itself and the resulting binary are not both cryptographically verified against known-good hashes.

**Verification**:

1. Monitor the browser update mechanism to detect delta update packages (smaller than full updates)
2. Verify that delta updates are offered only when the current version is compatible
3. Capture a delta update package and examine its structure and signature
4. Verify that delta updates are cryptographically signed independently from full updates
5. Test that applying a delta update includes verification of the resulting files against expected hashes
6. Attempt to apply a delta update to an incompatible base version and verify it is rejected
7. Test that delta update application includes atomic operations (all-or-nothing installation)
8. Verify that failed delta updates can fall back to full update downloads
9. Check that delta updates include integrity checks for both the patch and the result
10. Confirm that delta update security matches or exceeds full update security
11. Delta updates are cryptographically signed and verified before application
12. Source version verification ensures delta is compatible with installed version
13. Resulting files after delta application are verified against target hashes
14. Incompatible delta updates are rejected with fallback to full updates
15. Delta update application is atomic (complete or rollback)
16. Both patch integrity and result integrity are verified
17. Delta updates use same or stronger cryptography as full updates
18. Delta update failures trigger automatic fallback mechanisms

**Pass Criteria**: Delta updates are signed and verified independently AND source version compatibility is checked AND resulting files are verified against target hashes AND fallback to full updates on failure

**Fail Criteria**: Delta updates bypass security verification OR no source version checking OR result files not verified OR no fallback mechanism for failed deltas

**Evidence**: Delta update package analysis showing signatures, delta vs full update size comparisons, verification logs for delta application, test results from incompatible delta applications, fallback mechanism demonstrations, atomic operation verification

**References**:

- Google Courgette (Delta Compression): https://www.chromium.org/developers/design-documents/software-updates-courgette/
- Binary Diff Security: https://theupdateframework.github.io/specification/latest/#targets-metadata
- Mozilla MAR Format (Mozilla Archive): https://wiki.mozilla.org/Software_Update:MAR
- Microsoft Delta Updates: https://docs.microsoft.com/en-us/windows/deployment/update/psfxwhitepaper
- NIST Software Patch Security: https://csrc.nist.gov/glossary/term/patch

### Assessment: UPD-REQ-13 (Update server authentication)

**Reference**: UPD-REQ-13 - Browser shall authenticate update servers using certificate validation, pinning, and domain verification

**Given**: A conformant browser with UPD-1 or higher capability

**Task**: Verify that update server authentication prevents man-in-the-middle attacks and DNS hijacking attempts that could redirect browsers to malicious update servers distributing compromised builds. Certificate pinning and domain verification ensure that even if an attacker obtains a valid TLS certificate through a compromised Certificate Authority or DNS spoofing, the browser will reject connections to fraudulent update servers.

**Verification**:

1. Capture network traffic during update checks to identify update server domains
2. Examine TLS certificates presented by update servers for validity and chain of trust
3. Verify that update server domains match expected values hardcoded in browser or configuration
4. Test certificate pinning by attempting to present a valid but unpinned certificate for update domain
5. Attempt DNS spoofing to redirect update requests to malicious servers
6. Verify that update server certificate validation includes OCSP/CRL checks
7. Test that expired or revoked certificates for update servers are rejected
8. Check that update server authentication occurs before any update data is processed
9. Verify that update server domains use HSTS to prevent protocol downgrade attacks
10. Confirm that failed authentication prevents update checks and is logged
11. Update servers present valid TLS certificates with complete chain of trust
12. Certificate pinning is implemented for update server domains
13. Update server domains are verified against expected values
14. DNS spoofing attempts are detected through certificate pinning
15. Certificate revocation status is checked via OCSP or CRL
16. Expired or revoked certificates cause update failures
17. HSTS is enforced for update server domains
18. Authentication failures are logged and prevent update downloads

**Pass Criteria**: Update servers are authenticated with certificate validation AND certificate pinning is implemented AND domain verification prevents spoofing AND revocation checking is performed

**Fail Criteria**: No certificate pinning for update servers OR domain verification can be bypassed OR revocation checking is not performed OR expired certificates are accepted

**Evidence**: Update server TLS certificates and chains, certificate pinning configurations, network traces showing authentication, test results from DNS spoofing attempts, OCSP/CRL check logs, HSTS policy verification, authentication failure logs

**References**:

- Chrome Certificate Pinning: https://www.chromium.org/Home/chromium-security/security-faq/#TOC-How-does-key-pinning-work-in-Chrome-
- Certificate Transparency Monitoring: https://certificate.transparency.dev/
- IETF RFC 7469 Public Key Pinning: https://www.rfc-editor.org/rfc/rfc7469
- OCSP Stapling: https://www.rfc-editor.org/rfc/rfc6066#section-8
- Mozilla Update Server Security: https://wiki.mozilla.org/Security/Server_Side_TLS
- OWASP Certificate Pinning: https://owasp.org/www-community/controls/Certificate_and_Public_Key_Pinning

### Assessment: UPD-REQ-14 (Update timing jitter)

**Reference**: UPD-REQ-14 - Browser shall implement randomized timing jitter for update checks to prevent server load spikes and timing analysis

**Given**: A conformant browser with UPD-1 or higher capability

**Task**: Verify that update timing jitter prevents thundering herd problems that could enable denial-of-service attacks against update infrastructure or timing analysis attacks that reveal browser deployment patterns. Synchronized update checks from millions of browsers could overwhelm update servers or allow attackers to identify organizational update policies through traffic analysis, making randomized jitter a critical availability and privacy protection.

**Verification**:

1. Configure multiple browser instances (at least 10) with synchronized clocks
2. Monitor update check timing for each instance over a 24-hour period
3. Calculate the distribution of update check times relative to the scheduled interval
4. Verify that update checks are not synchronized across all instances
5. Measure the jitter range (randomization window) applied to update checks
6. Test that jitter is applied even when manual update checks are performed
7. Verify that jitter does not delay critical security updates beyond acceptable windows
8. Check that jitter implementation prevents timing analysis attacks
9. Test that jitter ranges are appropriate (e.g., ±1-2 hours for daily checks)
10. Confirm that jitter is cryptographically random, not predictable
11. Update checks include randomized timing jitter to distribute server load
12. Jitter range is appropriate for the update check frequency (typically ±10-20%)
13. Multiple instances do not synchronize update checks at same time
14. Jitter uses cryptographically secure random number generation
15. Critical updates can bypass jitter for immediate deployment when needed
16. Jitter prevents timing analysis attacks on update behavior
17. Jitter does not excessively delay important security updates
18. Update check distribution follows expected random distribution

**Pass Criteria**: Update checks include random jitter of at least ±10% of check interval AND jitter uses cryptographic randomness AND multiple instances show distributed check times AND critical updates can bypass jitter

**Fail Criteria**: No timing jitter implemented OR jitter is predictable OR all instances synchronize checks OR critical updates are delayed by jitter

**Evidence**: Update check timing logs from multiple instances, statistical analysis of check time distribution, jitter range configuration, randomness quality analysis, test results showing de-synchronized checks, critical update bypass demonstrations

**References**:

- Chrome Update Timing: https://chromium.googlesource.com/chromium/src/+/main/docs/updater/functional_spec.md#update-checks
- Thundering Herd Problem: https://en.wikipedia.org/wiki/Thundering_herd_problem
- NIST Randomness Recommendations: https://csrc.nist.gov/projects/random-bit-generation
- Google Omaha Protocol Timing: https://github.com/google/omaha/blob/main/doc/ServerProtocolV3.md#update-check-timing
- Load Balancing Best Practices: https://aws.amazon.com/architecture/well-architected/

### Assessment: UPD-REQ-15 (Background update enforcement)

**Reference**: UPD-REQ-15 - Browser shall enforce background update processes that continue even when browser is not actively running

**Given**: A conformant browser with UPD-2 or higher capability

**Task**: Verify that background update enforcement ensures security updates are applied even when users rarely launch the browser, preventing scenarios where unpatched browsers accumulate critical vulnerabilities. Without background updates, attackers can target users who infrequently use their browsers but still have them installed, exploiting the extended window of vulnerability between releases and actual patching.

**Verification**:

1. Close all browser windows completely to ensure browser is not running
2. Monitor system processes to verify background update service remains active
3. Wait for the scheduled update check interval with browser closed
4. Verify that update checks occur even when browser is not running
5. Test that background update service starts automatically at system boot
6. Simulate an available update and verify it downloads in background while browser is closed
7. Test that background updates can wake the system from sleep if configured (platform-dependent)
8. Verify that background update service has appropriate system permissions but runs with minimal privileges
9. Check that background update process is resistant to termination by users or malware
10. Confirm that background updates respect system resource constraints (network metering, battery status)
11. Background update service remains active when browser is closed
12. Update checks occur on schedule regardless of browser running state
13. Background service starts automatically at system boot
14. Updates can download and install without browser being open
15. Background service runs with minimal necessary privileges
16. Service cannot be easily disabled by users or malicious software
17. Resource-aware update behavior (respects metered connections, battery)
18. Background service restarts automatically if terminated abnormally

**Pass Criteria**: Background update service runs independently of browser AND performs update checks on schedule when browser closed AND downloads updates in background AND restarts automatically if terminated

**Fail Criteria**: Update service requires browser to be running OR no background update checks when closed OR service can be easily disabled OR does not restart after termination

**Evidence**: System process listings showing background service, update logs showing checks while browser closed, service configuration and permissions, automatic restart verification, resource usage monitoring, test results from service termination attempts

**References**:

- Chrome Background Updates: https://chromium.googlesource.com/chromium/src/+/main/docs/updater/functional_spec.md#background-mode
- Windows Update Service Architecture: https://docs.microsoft.com/en-us/windows/deployment/update/how-windows-update-works
- macOS Launch Agents: https://developer.apple.com/library/archive/documentation/MacOSX/Conceptual/BPSystemStartup/Chapters/CreatingLaunchdJobs.html
- Linux systemd Services: https://www.freedesktop.org/software/systemd/man/systemd.service.html
- Firefox Background Update Service: https://support.mozilla.org/en-US/kb/enable-background-updates-firefox-windows
- NIST Automated Patch Management: https://csrc.nist.gov/publications/detail/sp/800-40/rev-4/final

### Assessment: UPD-REQ-16 (Update notification UI)

**Reference**: UPD-REQ-16 - Browser shall provide clear, user-friendly notifications about available updates and security status without enabling user suppression of critical updates

**Given**: A conformant browser with UPD-1 or higher capability

**Task**: Verify that update notification UI balances security enforcement with user experience, ensuring critical security updates cannot be suppressed while avoiding notification fatigue that causes users to ignore all update prompts. This prevents social engineering attacks where users habitually dismiss security notifications and ensures that truly critical updates demanding immediate attention are distinguished from routine maintenance updates.

**Verification**:

1. Trigger an available update and observe the notification mechanism
2. Verify that update notifications are visible but non-intrusive (e.g., menu icon, subtle indicator)
3. Test that critical security updates generate more prominent notifications than feature updates
4. Attempt to dismiss or suppress update notifications and verify critical updates cannot be permanently suppressed
5. Verify that update notifications include clear information about update type (security vs feature)
6. Test that users can defer non-critical updates but not critical security updates
7. Check that update status is always accessible through browser settings or help menu
8. Verify that notifications include estimated update size and installation time
9. Test that update notifications are accessible (screen reader compatible, high contrast support)
10. Confirm that update UI clearly distinguishes between "check for updates" and current update status
11. Update notifications are displayed prominently but do not block browsing
12. Critical security updates have more prominent notifications than feature updates
13. Update type and importance are clearly communicated to users
14. Critical security updates cannot be permanently dismissed or ignored
15. Non-critical updates can be deferred by users with clear re-notification
16. Update status is always visible in browser settings/help menu
17. Notifications include helpful details (update size, type, installation requirements)
18. Update UI is accessible to users with disabilities
19. Clear distinction between available updates and current version status

**Pass Criteria**: Update notifications are clear and accessible AND critical updates cannot be permanently suppressed AND update type and importance are communicated AND users can defer non-critical updates

**Fail Criteria**: No update notifications OR critical updates can be permanently suppressed OR update type unclear OR notifications block browser usage OR inaccessible UI

**Evidence**: Screenshots of update notifications for various update types, test results from notification dismissal attempts, accessibility testing results (screen reader, high contrast), user flow documentation, notification timing and frequency logs

**References**:

- Chrome Update UI: https://support.google.com/chrome/answer/95414
- Firefox Update Preferences: https://support.mozilla.org/en-US/kb/update-firefox-latest-release
- WCAG 2.1 Accessibility Guidelines: https://www.w3.org/WAI/WCAG21/quickref/
- Microsoft UI Design Principles: https://docs.microsoft.com/en-us/windows/apps/design/
- NIST Usability and Security: https://www.nist.gov/itl/applied-cybersecurity/tig/back-basics-multi-factor-authentication

### Assessment: UPD-REQ-17 (Forced update for critical vulnerabilities)

**Reference**: UPD-REQ-17 - Browser shall support forced update mechanisms for critical vulnerabilities that require immediate patching

**Given**: A conformant browser with UPD-1 or higher capability

**Task**: Verify that forced update mechanisms can override user preferences when actively exploited critical vulnerabilities require immediate patching, preventing scenarios where user inaction leaves browsers vulnerable to widespread attacks. This emergency response capability is to be protected against abuse through cryptographic verification while ensuring that users running vulnerable versions are protected even if they attempt to defer updates.

**Verification**:

1. Review browser documentation for forced update or killswitch mechanisms
2. Simulate a critical vulnerability scenario requiring immediate update
3. Verify that forced updates can override user deferral preferences
4. Test that forced updates trigger mandatory browser restart with clear security messaging
5. Check that forced update status is indicated in update manifests with verifiable flags
6. Attempt to bypass or cancel a forced update and verify it cannot be avoided
7. Verify that forced updates include grace periods with countdown timers before enforcement
8. Test that forced updates can disable the browser if update fails or is unavailable
9. Check that forced update mechanism includes safeguards against abuse (signed manifests, trusted channels)
10. Confirm that forced update events are logged with justification and admin override options (if applicable)
11. Browser supports forced update mechanism for critical security issues
12. Forced updates override user preferences and deferral settings
13. Clear security messaging explains necessity of forced updates to users
14. Forced update flags in manifests are cryptographically verified
15. Grace periods provide countdown timers before mandatory restart
16. Forced updates cannot be bypassed or permanently cancelled
17. Browser may be disabled if critical update cannot be applied
18. Forced update mechanism is protected against spoofing and abuse
19. Enterprise environments may have limited admin override with logging

**Pass Criteria**: Forced update mechanism exists for critical vulnerabilities AND overrides user deferrals AND provides clear security messaging AND forced update flags are cryptographically verified AND includes grace periods

**Fail Criteria**: No forced update mechanism OR can be bypassed by users OR no verification of forced update flags OR no security messaging explaining necessity

**Evidence**: Forced update configuration documentation, test results from simulated critical updates, user notification screenshots, forced update manifest flags, grace period timer demonstrations, bypass attempt results, audit logs for forced updates

**References**:

- Chrome Component Killswitch: https://www.chromium.org/administrators/policy-list-3#ComponentUpdatesEnabled
- Firefox Blocklist System: https://wiki.mozilla.org/Blocklisting
- Microsoft Forced Update Policies: https://docs.microsoft.com/en-us/deployedge/microsoft-edge-update-policies#updatedefault
- CVE Critical Severity Guidelines: https://www.first.org/cvss/
- NIST Critical Patch Management: https://csrc.nist.gov/publications/detail/sp/800-40/rev-4/final

### Assessment: UPD-REQ-18 (Update verification chain)

**Reference**: UPD-REQ-18 - Browser shall implement complete chain-of-trust verification from update manifest through component signatures to final installation

**Given**: A conformant browser with UPD-1 or higher capability

**Task**: Verify that complete chain-of-trust verification prevents sophisticated supply chain attacks where attackers compromise individual components of the update distribution system. By requiring cryptographic validation at every level from root keys through manifests to individual component signatures, the browser ensures that compromise of any single element in the distribution chain cannot result in installation of malicious updates.

**Verification**:

1. Trace the complete update verification chain from initial update check to installation
2. Verify that update manifest is signed by trusted root key embedded in browser
3. Examine the signature chain: root key → manifest → component hashes → component signatures
4. Test that each level of the verification chain is validated before proceeding
5. Attempt to break the chain by presenting valid components with invalid manifest
6. Verify that intermediate certificate revocation breaks the verification chain
7. Test that the root keys used for update verification are embedded in browser binary and protected
8. Check that chain-of-trust validation occurs even for component updates
9. Verify that the entire verification chain is logged for audit purposes
10. Confirm that any break in verification chain prevents installation and triggers errors
11. Complete chain-of-trust from root keys to installed components
12. Root keys for update verification are embedded in browser binary
13. Update manifests are signed and verified against trusted root keys
14. Component signatures are verified against manifest hashes
15. Each verification step is performed in sequence with no shortcuts
16. Any break in verification chain prevents installation
17. Intermediate certificate revocation is detected and enforced
18. Verification chain is logged with details at each step
19. Chain-of-trust applies to both full and component updates

**Pass Criteria**: Complete verification chain from root keys to components AND each level is validated before proceeding AND breaks in chain prevent installation AND root keys are embedded and protected

**Fail Criteria**: Incomplete verification chain OR steps can be skipped OR root keys not embedded OR chain breaks do not prevent installation

**Evidence**: Verification chain documentation and diagrams, root key extraction from browser binary, signature verification logs at each chain level, test results from chain break attempts, intermediate certificate revocation tests, audit logs showing complete chain verification

**References**:

- Chrome Root Certificate Program: https://www.chromium.org/Home/chromium-security/root-ca-policy/
- Code Signing Certificate Chains: https://docs.microsoft.com/en-us/windows-hardware/drivers/install/digital-signatures
- X.509 Certificate Path Validation: https://www.rfc-editor.org/rfc/rfc5280#section-6
- Mozilla Root Store Policy: https://www.mozilla.org/en-US/about/governance/policies/security-group/certs/policy/
- TUF Root of Trust: https://theupdateframework.github.io/specification/latest/#root-metadata
- NIST Trust Anchor Management: https://csrc.nist.gov/publications/detail/sp/800-57-part-1/rev-5/final

### Assessment: UPD-REQ-19 (Update source pinning)

**Reference**: UPD-REQ-19 - Browser shall implement update source pinning to prevent malicious redirection to unauthorized update servers

**Given**: A conformant browser with UPD-1 or higher capability

**Task**: Verify that update source pinning prevents malicious redirection attacks that could deliver compromised updates through DNS hijacking, BGP routing attacks, or compromised enterprise proxies. Hardcoded, pinned update server domains ensure that even if network infrastructure is compromised, browsers will only accept updates from authentic vendor-controlled servers validated through certificate pinning.

**Verification**:

1. Identify the configured update server URLs embedded in browser binary or configuration
2. Verify that update server domains are pinned and cannot be modified through configuration files
3. Attempt to modify system DNS or hosts file to redirect update domains to malicious servers
4. Test that certificate pinning for update domains prevents MITM attacks
5. Verify that update server URLs use multiple trusted domains with fallback mechanisms
6. Attempt to inject malicious update server URLs through registry/preference modifications
7. Test that update source pinning is enforced even for enterprise-managed deployments
8. Check that hardcoded update domains cannot be overridden by network-based attacks
9. Verify that fallback update servers are also pinned and verified
10. Confirm that update source pinning violations are logged and reported
11. Update server domains are hardcoded in browser binary
12. Update source URLs cannot be modified through configuration or registry
13. DNS redirection attacks are prevented through certificate pinning
14. Multiple trusted update domains with verified fallback mechanisms
15. Enterprise policies cannot override update source pinning for security updates
16. Network-based redirection attempts are detected and blocked
17. Fallback servers are subject to same pinning requirements
18. Source pinning violations are logged as security events

**Pass Criteria**: Update server domains are hardcoded AND cannot be modified by configuration OR DNS attacks AND certificate pinning prevents redirection AND fallback servers are also pinned

**Fail Criteria**: Update servers can be modified through configuration OR DNS redirection succeeds OR no certificate pinning OR enterprise policies can override source pinning

**Evidence**: Decompiled browser binary showing hardcoded update URLs, test results from DNS redirection attempts, certificate pinning verification, configuration modification tests, enterprise policy override tests, source pinning violation logs

**References**:

- Chrome Update Server Infrastructure: https://chromium.googlesource.com/chromium/src/+/main/docs/updater/protocol_3_1.md#update-server
- Certificate Pinning Implementation: https://owasp.org/www-community/controls/Certificate_and_Public_Key_Pinning
- DNS Rebinding Protection: https://en.wikipedia.org/wiki/DNS_rebinding
- Mozilla Update Server Security: https://wiki.mozilla.org/Software_Update#Security
- Google Omaha Server Protocol: https://github.com/google/omaha/blob/main/doc/ServerProtocolV3.md
- NIST Supply Chain Risk Management: https://csrc.nist.gov/Projects/cyber-supply-chain-risk-management

### Assessment: UPD-REQ-20 (Update integrity verification)

**Reference**: UPD-REQ-20 - Browser shall verify integrity of installed components after update application to detect corruption or tampering

**Given**: A conformant browser with UPD-1 or higher capability

**Task**: Verify that post-installation integrity verification detects tampering or corruption that occurs after updates are applied, protecting against attacks where malware modifies browser components between installation and execution. This closes the security window where installed files are vulnerable to modification before integrity checks run, ensuring that any tampering triggers immediate remediation.

**Verification**:

1. Perform a complete browser update and monitor the post-installation verification phase
2. Verify that installed files are checked against expected cryptographic hashes after installation
3. Attempt to modify an installed file immediately after update completion
4. Test that modified files are detected on next browser launch
5. Verify that integrity verification occurs both after installation and at browser startup
6. Check that integrity verification covers all critical components (binaries, libraries, resources)
7. Test that integrity failures trigger repair or re-installation mechanisms
8. Verify that integrity verification results are logged with specific failure details
9. Test that browser refuses to launch if critical component integrity verification fails
10. Confirm that integrity verification uses same cryptographic strength as update verification (SHA-256+)
11. Post-installation integrity verification checks all installed components
12. Cryptographic hashes (SHA-256+) are used for integrity verification
13. Modified files are detected immediately after installation
14. Startup integrity checks detect tampering between sessions
15. Critical components are verified (binaries, libraries, key resources)
16. Integrity failures trigger automatic repair or update mechanisms
17. Browser refuses to launch if critical components fail verification
18. Integrity verification results are logged with specific error details
19. Verification coverage includes all security-critical components

**Pass Criteria**: Post-installation integrity verification is performed AND uses strong cryptographic hashes (SHA-256+) AND modified files are detected AND integrity failures trigger repair OR prevent launch

**Fail Criteria**: No post-installation verification OR weak hash algorithms OR modified files not detected OR integrity failures do not trigger corrective actions

**Evidence**: Post-installation verification logs, hash algorithm analysis, test results from file modification attacks, startup integrity check logs, repair mechanism demonstrations, critical component verification coverage analysis

**References**:

- Chrome Component Integrity Verification: https://www.chromium.org/Home/chromium-security/education/tls#TOC-Certificate-Verification
- Windows Code Integrity: https://docs.microsoft.com/en-us/windows/security/threat-protection/windows-defender-application-control/windows-defender-application-control
- macOS Gatekeeper and Code Signing: https://developer.apple.com/documentation/security/notarizing_macos_software_before_distribution
- Linux Integrity Measurement Architecture: https://sourceforge.net/p/linux-ima/wiki/Home/
- NIST File Integrity Monitoring: https://csrc.nist.gov/glossary/term/file_integrity_monitoring
- OWASP Software Component Verification: https://owasp.org/www-project-software-component-verification-standard/

### Assessment: UPD-REQ-21 (Staged rollout support)

**Reference**: UPD-REQ-21 - Browser shall support staged rollout mechanisms to gradually deploy updates to user populations with rollback capability

**Given**: A conformant browser with UPD-2 or higher capability

**Task**: Verify that staged rollout mechanisms limit the blast radius of defective updates while maintaining rapid response capability for critical security fixes. Gradual deployment with rollback capability prevents scenarios where buggy updates simultaneously impact millions of users, while emergency bypass ensures that actively exploited vulnerabilities can still be patched immediately across the entire user base.

**Verification**:

1. Review browser update architecture for staged rollout or canary deployment support
2. Verify that update manifests include rollout percentage or cohort targeting information
3. Test that updates are delivered to progressively larger user populations over time
4. Check that rollout stages are controlled by server-side configuration, not client manipulation
5. Verify that users cannot force-join or opt-out of rollout cohorts
6. Test that rollout can be paused or rolled back if issues are detected
7. Monitor multiple browser instances to observe different rollout timing
8. Verify that critical security updates can bypass staged rollout for immediate deployment
9. Test that rollout cohorts are assigned using stable user identifiers (not random per check)
10. Confirm that staged rollout status is logged for monitoring and analysis
11. Update system supports staged rollout with progressive deployment
12. Rollout percentages are specified in update manifests and enforced server-side
13. Users cannot manipulate rollout cohort assignment
14. Rollout can be paused or reversed if issues are detected
15. Critical security updates can bypass staged rollout
16. Cohort assignment is stable (same user gets consistent rollout timing)
17. Multiple instances show varied rollout timing based on cohort
18. Rollout status and cohort information are logged
19. Rollout progression follows defined stages (e.g., 1%, 10%, 50%, 100%)

**Pass Criteria**: Staged rollout mechanism is implemented AND rollout percentages are server-controlled AND users cannot manipulate cohorts AND critical updates can bypass rollout AND rollback capability exists

**Fail Criteria**: No staged rollout support OR users can manipulate rollout OR all users receive updates simultaneously OR no rollback capability OR critical updates follow slow rollout

**Evidence**: Update manifest files showing rollout percentages, server-side rollout configuration documentation, test results from multiple instances showing varied timing, rollout logs with cohort information, critical update bypass demonstrations, rollback process documentation

**References**:

- Chrome Staged Rollout: https://chromium.googlesource.com/chromium/src/+/main/docs/updater/functional_spec.md#staged-rollout
- Google Omaha Rollout Mechanisms: https://github.com/google/omaha/blob/main/doc/ServerProtocolV3.md#rollout
- Canary Deployments: https://martinfowler.com/bliki/CanaryRelease.html
- Progressive Delivery Patterns: https://www.split.io/glossary/progressive-delivery/
- NIST Phased Deployment: https://csrc.nist.gov/publications/detail/sp/800-40/rev-4/final

### Assessment: UPD-REQ-22 (Update domain validation)

**Reference**: UPD-REQ-22 - Browser shall validate that update requests and responses originate from authorized domains with strict certificate requirements

**Given**: A conformant browser with UPD-1 or higher capability

**Task**: Verify that update domain validation prevents server-side request forgery and domain confusion attacks where attackers redirect update requests to malicious servers through HTTP redirects, DNS manipulation, or compromised network infrastructure. Strict domain allowlisting ensures that browsers only download updates from explicitly authorized vendor domains, rejecting any deviation regardless of certificate validity.

**Verification**:

1. Capture update network traffic to identify all domains involved in update process
2. Verify that all update domains are whitelisted or hardcoded in browser configuration
3. Examine TLS certificates for update domains to verify they meet strict requirements (EV or equivalent)
4. Attempt to redirect update requests to unauthorized domains using DNS attacks
5. Test that update domain acceptlist cannot be modified by users or malware
6. Verify that update responses from unauthorized domains are rejected
7. Check that update domain validation includes subdomain restrictions (no wildcards)
8. Test that HTTP redirects to unauthorized domains during update process are rejected
9. Verify that update domain validation occurs for all update-related requests (manifests, downloads, telemetry)
10. Confirm that domain validation failures are logged with domain details
11. All update domains are explicitly whitelisted or hardcoded
12. TLS certificates for update domains meet strict requirements
13. Unauthorized domains are rejected even with valid TLS certificates
14. Domain acceptlist cannot be modified through configuration or registry
15. Subdomain validation is strict (no wildcard matching)
16. HTTP redirects to unauthorized domains are blocked
17. Domain validation applies to all update-related traffic
18. Validation failures are logged with attempted domain information
19. Update domain list is protected and verified at startup

**Pass Criteria**: Update domains are whitelisted/hardcoded AND unauthorized domains are rejected AND domain list cannot be modified AND validation applies to all update traffic AND redirects to unauthorized domains are blocked

**Fail Criteria**: No domain acceptlist OR unauthorized domains accepted OR domain list can be modified OR validation can be bypassed with redirects OR logging insufficient

**Evidence**: Network traffic captures showing update domains, domain acceptlist extraction from browser binary, test results from unauthorized domain redirects, TLS certificate analysis, domain validation logs, configuration modification attempt results

**References**:

- Chrome Update Domain Security: https://chromium.googlesource.com/chromium/src/+/main/docs/updater/protocol_3_1.md#security
- Mozilla Update Domain Policies: https://wiki.mozilla.org/Software_Update#Security
- DNS Security Extensions (DNSSEC): https://www.icann.org/resources/pages/dnssec-what-is-it-why-important-2019-03-05-en
- Extended Validation Certificates: https://en.wikipedia.org/wiki/Extended_Validation_Certificate
- OWASP Server-Side Request Forgery Prevention: https://cheatsheetseries.owasp.org/cheatsheets/Server_Side_Request_Forgery_Prevention_Cheat_Sheet.html
- NIST Domain Validation Guidelines: https://csrc.nist.gov/publications/detail/sp/800-63/3/final

### Assessment: UPD-REQ-23 (Update binary reproducibility)

**Reference**: UPD-REQ-23 - Browser shall support mechanisms to enable verification of binary reproducibility for update transparency and supply chain security

**Given**: A conformant browser with UPD-2 or higher capability

**Task**: Verify that binary reproducibility enables independent verification of update authenticity, protecting against sophisticated supply chain attacks where build infrastructure is compromised to inject backdoors. Reproducible builds allow security researchers and organizations to verify that distributed binaries match published source code, detecting unauthorized modifications introduced during compilation or packaging.

**Verification**:

1. Review browser build and release documentation for reproducible build support
2. Verify that update packages include build metadata (compiler version, build timestamp, source commit)
3. Attempt to reproduce an official update binary from published source code using documented build process
4. Compare reproduced binary hash with official release hash to verify reproducibility
5. Check that build process documentation includes all dependencies and toolchain versions
6. Verify that update transparency logs include binary hashes for independent verification
7. Test that multiple independent parties can reproduce identical binaries from same source
8. Check for availability of build attestations or signed build manifests
9. Verify that non-reproducible elements (timestamps, randomness) are minimized or eliminated
10. Confirm that reproducibility documentation and verification tools are publicly available
11. Browser supports reproducible builds with documented build process
12. Update packages include complete build metadata
13. Independent verification of binary reproducibility is possible
14. Build process documentation includes all dependencies and toolchain versions
15. Multiple builds from same source produce bit-identical binaries
16. Update transparency logs enable third-party verification
17. Non-deterministic build elements are minimized or documented
18. Build attestations or signed manifests are available
19. Public documentation and tools support reproducibility verification

**Pass Criteria**: Reproducible build process is documented AND build metadata is included in updates AND independent parties can verify binary reproducibility AND update transparency supports third-party verification

**Fail Criteria**: No reproducible build support OR build process not documented OR independent verification not possible OR build metadata missing OR excessive non-deterministic elements

**Evidence**: Build process documentation, reproduced binary hash comparisons, build metadata extraction from update packages, transparency log entries, independent build verification results, build attestation signatures, reproducibility verification tool outputs