firestore-rules-audit

name	firestore-rules-audit
description	Audit Firestore security rules for public access, semantic errors, unsafe match-block composition, and missing validation. Use when the user asks to review firestore.rules, check rules for vulnerabilities, or explain why a rule allows/denies an operation.

Firestore Rules Audit

Answer three questions about a ruleset, with evidence:

1. Who can do what? (access analysis)
2. Do the expressions work in their operation context? (semantic validity)
3. Do the match blocks compose safely? (structural analysis)

Steps

1. Read the ruleset. Use the project's firestore.rules, or firestore_get_rules for deployed state. Complete when you can list every match block and the operations each allows.

2. Lint. Run firestore_lint_rules. Complete when every lint finding is either carried into the report or explained away.

3. Access analysis. For each match block, record identity × operation (get/list/create/update/delete) → allow/deny. Flag public writes, public reads on sensitive paths, and create/update/delete without an auth check. Complete when the access matrix has no blank cells.

4. Semantic checks. Verify each expression against its operation context:

   • list cannot rely on a single document's resource.data — a list query must be constrained so it can only return readable documents.
   • create reads request.resource.data; there is no resource.data yet.
   • Authorization derives from resource.data (what exists); the writer controls request.resource.data, so validation — not authorization — reads it.

   Complete when every resource.data / request.resource.data use is justified for its operation.

5. Composition checks. Any matching allow grants access — permissive wildcards override specific restrictions elsewhere. Flag recursive wildcards ({doc=**}) that bypass sibling rules, undefined function calls, unused functions whose names near-miss a called one, and repeated get()/exists() calls that multiply per-request cost. Complete when every wildcard's reach is stated.

6. Prove the findings. Back each critical/high finding with firestore_simulate_rules (vary auth context and operation) or a firestore_test_rules suite; pyric_derive_rules_test_cases can generate the case list. Complete when each such finding cites a passing simulation/test demonstrating the problem.

7. Report.

   ## Firestore Rules Audit
   ### Summary
   ### Findings            (grouped critical → low, each with evidence + fix)
   ### Positive Observations
   ### Recommended Fixes
   

If the user asks for remediation: change the rules, re-lint, then re-run the simulations or tests that exposed each finding and confirm they now deny.

Reference — high-signal patterns

• allow write: if true or allow write: if request.auth != null on user-owned data — critical or high depending on path sensitivity.
• Validation absent on any user-controlled create/update — high.
• request.auth.uid == resource.data.ownerId on create — broken (no resource yet); the intent needs request.resource.data.ownerId plus a uid check.
• Role fields writable by the user they empower — privilege escalation.