NavSentinel is a defensive browser extension. Its job is to make common navigation and credential-deception paths harder to execute quietly.

The most security-sensitive code lives in:

• extension/src/content/main_guard.ts
• extension/src/content/capture_isolated.ts
• extension/src/content/credential_guard.ts
• extension/src/shared/domain.ts
• extension/src/shared/storage.ts
• extension/src/sw/sw.ts

• steady-state relaying uses a transferred MessagePort scoped to the current document/frame rather than ordinary page-visible messages
• challenge-response proves liveness and possession of the transferred port; it does not authenticate an isolated-world identity against hostile same-page code, so document-start ordering remains a mitigation and #175/#186 block beta
• per-document session and schema checks reject stale/cross-document traffic
• explicit inbound message-type allowlists
• replayable blocked actions with short-lived ids
• no authorization decision should rely on an arbitrary page-originated message

• popup and redirect allowance windows are time-limited
• blocked actions expire quickly
• rollback exists as a recovery path for suspicious committed navigations
• allowlists are site-scoped rather than global

• password submits are intercepted before dispatch completes
• risk and destination are evaluated before a blocked submit can resume
• trusted domains are stored locally and scoped to registrable domains
• paste warnings discourage silent use of saved secrets on untrusted surfaces

• local-only storage
• bounded event log retention
• normalization and migration of older key shapes

• event logging is best-effort because chrome.storage.local is not transactional
• domain normalization uses a build-time PSL snapshot; new TLDs require a data rebuild
• page-injected navigation/credential prompts currently expose protection- lowering actions to page-controlled placement and scripted activation. RI-01 blocks beta until injected UI is warn/cancel only and extension-origin UI owns every proceed/allow/trust/resume decision with tab/destination binding and TTL
• the release-eligible interaction-only profile has no reputation runtime, asset, or claim. A deterministic 15-domain .example fixture remains only in the explicit unpacked research profile, which package and release checks reject
• a browser extension cannot defend against a fully compromised browser or OS

If a bug could materially weaken the extension's protections, use the private vulnerability report instead of opening a public issue. GitHub private vulnerability reporting is enabled for this repository; the report and follow-up remain private to the reporter and repository maintainers until coordinated disclosure is appropriate.

When reporting, include:

• affected file paths
• reproduction steps
• expected and actual behavior
• whether the issue affects navigation protection, credential protection, or both