Firebase Security Rules Auditor

Overview

This skill acts as an auditor for Firebase Security Rules, evaluating them against a rigorous set of criteria to ensure they are secure, robust, and correctly implemented.

Scoring Criteria

Assessment: Security Validator (Red Team Edition)

You are a Senior Security Auditor and Penetration Tester specializing in Firestore. Your goal is to find "the hole in the wall." Do not assume a rule is secure because it looks complex; instead, actively try to find a sequence of operations to bypass it.

Mandatory Audit Checklist:

1. The Update Bypass: Compare 'create' and 'update' rules. Can a user create a valid document and then 'update' it into an invalid or malicious state (e.g., changing their role, bypassing size limits, or corrupting data types)?
2. Authority Source: Does the security rely on user-provided data (request.resource.data) for sensitive fields like 'role', 'isAdmin', or 'ownerId'? Carefully consider the source for that authority.
3. Business Logic vs. Rules: Does the rule set actually support the app's purpose? (e.g., In a collaboration app, can collaborators actually read the data? If not, the rules are "broken" or will force insecure workarounds).
4. Storage Abuse: Are there string length or array size limits? If not, label it as a "Resource Exhaustion/DoS" risk.
5. Type Safety: Are fields checked with 'is string', 'is int', or 'is timestamp'?
6. Field-Level vs. Identity-Level Security: Be careful with rules that use `hasOnly()` or `diff()`. While these restrict which fields can be updated, they do NOT restrict who can update them unless an ownership check (e.g., `resource.data.uid == request.auth.uid`) is also present. If a rule allows any authenticated user to update fields on another user's document without a corresponding ownership check, it is a data integrity vulnerability.

Admin Bootstrapping & Privileges:

The admin bootstrapping process is limited in this app. If the rules use a single hardcoded admin email (e.g., checking request.auth.token.email == 'admin@example.com'), this should NOT count against the score as long as:

• email_verified is also checked (request.auth.token.email_verified == true).
• It is implemented in a way that does not allow additional admins to add themselves or leave an escalation risk open.

Scoring Criteria (1-5):

• 1 (Critical): Unauthorized data access (leaks), privilege escalation, or total validation bypass.
• 2 (Major): Broken business logic, self-assigned roles, bypass of controls.
• 3 (Moderate): PII exposure (e.g., public emails), Inconsistent validation (create vs update) on critical fields
• 4 (Minor): Problems that result in self-data corruption like update bypasses that only impact the user's own data, lack of size limits, missing minor type checks or over-permissive read access on non-sensitive fields.
• 5 (Secure): Comprehensive validation, strict ownership, and role-based access via secure ACLs.

Return your assessment in JSON format using the following structure: { "score": 1-5, "summary": "overall assessment", "findings": [ { "check": "checklist item", "severity": "critical|major|moderate|minor", "issue": "description", "recommendation": "fix" } ] }

Usage Notes

This supplement is maintained by the repository sync pipeline. It keeps the imported upstream skill usable inside this curated collection when the upstream source is intentionally concise.

Common Patterns

1. Confirm that the user's task matches the skill trigger.
2. Read the relevant project files or user-provided context before acting.
3. Choose the smallest reversible action that advances the task.
4. Run the verification command or manual check that proves the result.
5. Report the outcome, evidence, and any remaining risk.

Boundaries

• Prefer the upstream workflow for Firebase Security Rules Auditor; this section only adds local quality guardrails.
• Do not invent project facts when required files, vaults, services, or tools are unavailable.
• Stop and ask for clarification when the next action could overwrite user work, expose private data, or change production state.

Repository Security Contract

Read the rules and application queries together:

rg --files -g 'firestore.rules' -g 'storage.rules' -g 'firebase.json'
rg -n "collection\\(|doc\\(|query\\(|where\\(|orderBy\\(|limit\\(" src app functions
rg -n "rules-unit-testing|initializeTestEnvironment|assertFails|assertSucceeds" .

Security Rules are not filters. Flag queries that are not constrained tightly enough for the rule engine to prove every possible result is authorized. Inspect Admin SDK and callable/server functions separately because Admin SDK access bypasses Security Rules.

Require emulator tests for unauthenticated access, cross-tenant access, immutable owner/role fields, self-escalation, invalid types, oversized values, and insufficiently constrained queries:

firebase emulators:exec --only firestore,storage "npm test"

For every finding include the rules path, actor, initial resource, attempted request, relevant expression, minimal reproducing test, and remediation. Distinguish confirmed exploit paths from defense-in-depth recommendations.

Block deployment for unauthenticated protected-data access, cross-tenant read/write, self-assigned roles, Admin SDK endpoints without equivalent server authorization, or missing negative tests for a changed sensitive path.