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+---
+phase: "19"
+slug: "chat-and-chatchannels"
+status: verified
+# threats_open = count of OPEN threats at or above workflow.security_block_on severity (the blocking gate)
+threats_open: 0
+asvs_level: 1
+created: "2026-10-28"
+---
+
+# Phase 19 — Security
+
+> Per-phase security contract: threat register, accepted risks, and audit trail.
+
+Implementation lives in the sibling repos `sm-chat-plugin` and `sm-chatchannels-plugin`; the user-namespace authorizer and `user.Deleting` event are in `sm-user-plugin` v0.1.2. Paths below are relative to the meta repo.
+
+---
+
+## Trust Boundaries
+
+| Boundary | Description | Data Crossing |
+|----------|-------------|---------------|
+| client → /_chat/api/v1, /_chatchannels/api/v1 | untrusted JSON, ids and multipart files cross jwt.auth | message bodies, attachment bytes, conversation ids |
+| ChatService write → Postgres | authenticated actor ids become conversation and message rows | user-authored content |
+| ChatService → lighthouse / Centrifugo | realtime payloads cross to subscribers | event payloads (ids only) |
+| Authorizer → subscribe | client-chosen channel string trusted only after participant check | channel names |
+| download handler → blob store | private system_files bytes leave only after a participation check | private attachments |
+| DM start → other users | unsolicited conversation creation | conversation rows |
+| ChannelService → resolver | host-installed access policy; default deny-all | context access decisions |
+| mention body → users.handle | untrusted @tokens become mention rows | user ids |
+| user delete → chat/channel tables | GDPR cascade must not leave prefs/members or wipe others' rows | personal data |
+| golden files / check-phase19.sh → CI | recorded PHP payloads and sibling paths become the acceptance oracle | test oracle |
+
+---
+
+## Threat Register
+
+| Threat ID | Category | Component | Severity | Disposition | Mitigation | Status |
+|-----------|----------|-----------|----------|-------------|------------|--------|
+| T-19-01 | Information disclosure | api/download.go, message GET | high | mitigate | `sm-chat-plugin/api/download.go` collapses missing/unauthorized to `writeNotFound`; `AttachmentForDownload` checks `CanView`; `TestAttachmentDownload` (http_tracer_test.go:340) | closed |
+| T-19-02 | Elevation of privilege | api/dm.go | medium | mitigate | `chat-dm` bucket Max 10 / minute (routes.go:69); `TestDMThrottle` in PG_CHAT_TESTS | closed |
+| T-19-03 | Tampering | classes/attachment_policy.go | high | mitigate | `MaxAttachments = 5`, `MaxAttachmentBytes`, `BannedExts` svg/html/xml + banned MIME list; `TestAttachmentPolicy` | closed |
+| T-19-04 | Information disclosure | lighthouse Bind payload | high | mitigate | ids-only broadcast payload; `TestChatTracer` (tracer_test.go:17) and golden_test.go fail if a publication contains `content` | closed |
+| T-19-05 | Elevation of privilege | classes/authorizer.go | high | mitigate | parses `chat:conversation:{id}` (one optional presence: prefix), `Denied("not a participant")`, capabilities `["prs"]`, checked per subscribe | closed |
+| T-19-06 | Elevation of privilege | classes/mention_parser.go | high | mitigate | `ResolveMentionedParticipantIDs` joins `golem15_chat_participants` for the conversation and excludes `senderID` (channel_service.go:1158) | closed |
+| T-19-07 | Information disclosure | user.Deleting → SeverUserFromContext | high | mitigate | `FireDeletingEvent` fires inside the delete tx (sm-user-plugin controllers/users_admin_controller.go:525); chatchannels `onUserDeleting` → `SeverUserFromContext`; `TestDeletingCascade` | closed |
+| T-19-08 | Denial of service | classes/search_indexer.go | medium | mitigate | index/deindex errors logged at Warn, never returned (fail-open); `TestSearchIndexer` | closed |
+| T-19-09 | Elevation of privilege | api/attachments.go pending field | high | mitigate | `PendingField(actorID)` = `chat-pending-{actorID}`; claiming another actor's pending row refused (classes/attachments.go:22) | closed |
+| T-19-10 | Elevation of privilege | user namespace authorizer | high | mitigate | sm-user-plugin `AuthorizeUser` allows only `user:{id}` for that user, rejects double presence/extra segments; `RegisterUserAuthorizer` skips if registered; `TestUserAuthorizer` in check-phase19.sh | closed |
+| T-19-11 | Denial of service | mention regex | medium | mitigate | RE2 `@([A-Za-z0-9_.-]{2,255})`, bounded, no nested quantifiers (mention_parser.go:8) | closed |
+| T-19-12 | Elevation of privilege | DenyAll + Boot Warn | medium | mitigate | `DenyAll` returns false for both methods; boot.go:64 Warns while resolver is deny-all | closed |
+| T-19-13 | Information disclosure | TestGoldenEvents | high | mitigate | golden_test.go:241 fails when a publication payload contains key `content` | closed |
+| T-19-14 | Elevation of privilege | mention resolve | high | mitigate | participant-only handle match (same query as T-19-06); `TestHandleMention` (sm-chatchannels-plugin http_tracer_test.go:37) | closed |
+| T-19-15 | Elevation of privilege | classes/service.go canSend | high | mitigate | `canSend` returns `isParticipant` only (service.go:304); `ErrNotParticipant` mapped to 404 (api/errors.go:57); `TestGapClosureSmoke`, `TestTeammateDMWriteIDOR` | closed |
+| T-19-16 | Tampering | user.Deleting → created_by CASCADE | high | mitigate | chat `onUserDeleting` → `ReassignCreatedBy` in the Deleting tx (boot.go:187, service.go:115); baseline CASCADE untouched | closed |
+| T-19-17 | Elevation of privilege | TestTeammateDMWriteIDOR + PG_CHAT_TESTS | high | mitigate | listed in `PG_CHAT_TESTS` and in the self-test required tokens of scripts/check-phase19.sh | closed |
+| T-19-18 | Tampering | TestDeletingCascade creator path | high | mitigate | test fires Deleting then `Unscoped` deletes Alice (http_tracer_test.go:301); `TestDeletingCascade` in `PG_CHATCHANNELS_TESTS` | closed |
+| T-19-SC | Tampering | go.mod requires, scripts/check-phase19.sh | high | mitigate | plugin direct requires (gormigrate, pgx, testcontainers, gocloud.dev, gorm) are the framework's pinned versions plus Golem15 modules; gate installs no packages and `--self-test` plants failures | closed |
+
+*Status: open · closed · open — below high threshold (non-blocking)*
+*Severity: critical > high > medium > low — only open threats at or above workflow.security_block_on count toward threats_open*
+*Disposition: mitigate (implementation required) · accept (documented risk) · transfer (third-party)*
+
+---
+
+## Accepted Risks Log
+
+No accepted risks.
+
+---
+
+## Security Audit Trail
+
+| Audit Date | Threats Total | Closed | Open | Run By |
+|------------|---------------|--------|------|--------|
+| 2026-10-28 | 19 | 19 | 0 | /msd-secure-phase (orchestrator, ASVS L1 grep verification) |
+
+---
+
+## Sign-Off
+
+- [x] All threats have a disposition (mitigate / accept / transfer)
+- [x] Accepted risks documented in Accepted Risks Log
+- [x] `threats_open: 0` confirmed
+- [x] `status: verified` set in frontmatter
+
+**Approval:** verified 2026-10-28