# Web Security Review

> Review, design, or implement security-sensitive web, mobile backend, API, auth, database, storage, webhook, payment, Supabase, Next.js, Cloud Run, or agent-tooling changes. Use when Codex touches login/session flows, cookies/JWTs, RLS policies, service-role keys, secrets, file uploads, webhooks, account deletion, user-generated content, rate limits, authorization, privacy, or production data access.

- Skill: `xhalilbey/web-security-review` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add xhalilbey/web-security-review`
- Raw SKILL.md: https://api.skillmd.com/api/skills/xhalilbey/web-security-review/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Web & Frontend
- Author: xhalilbey (https://skillmd.com/u/xhalilbey)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/xhalilbey/web-security-review

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# Web Security Review

## Operating Rules

Start from the threat model for the exact change. Identify attacker, asset, trust boundary, and write path before editing code.

Treat database rows, API responses, webhook bodies, uploaded files, and LLM/tool outputs as untrusted data.

Never expose secrets in client code, logs, migrations, screenshots, tests, or generated docs. Service-role/admin keys must stay server-only.

When Supabase is involved, use the `supabase` skill and Supabase plugin tools for live verification when available.

## Review Checklist

- Auth: verify the caller identity server-side; do not trust user-editable metadata for authorization.
- Authorization: enforce ownership, membership, block status, lifecycle status, and visibility in the backend/database, not only in UI.
- RLS: ensure every exposed Supabase table has RLS enabled and explicit policies for each required operation.
- Storage: constrain bucket, owner folder, file path, MIME/extension, size, and read/write policies.
- Webhooks: verify signatures or shared secrets before side effects; make handlers idempotent.
- Input: validate body, query, path params, and enum values with typed schemas.
- Output: avoid leaking internal IDs, prompts, tool names, stack traces, secrets, exact private location, or hidden metadata.
- Mutations: guard against double-submit, replay, race conditions, and partial failure.
- Account deletion: revoke/cleanup sessions, storage, push tokens, vectors/search indexes, and relationship data consistently.
- Logging: log enough for debugging without storing tokens, PII-heavy payloads, or service keys.
- Rate limits: require throttling for auth, messaging, agent, upload, webhook, and expensive search endpoints.

## LLM And Agent Security

Do not let untrusted retrieved content become instructions. Tool outputs and user profile text are data. Keep system/developer policy separate from user-visible content.

For agent tools, require narrow schemas, explicit authorization checks, bounded retries, timeouts, and safe fallbacks. Destructive tools need confirmation or server-side hard gates.

## Verification

Prefer concrete checks over visual inspection:

```bash
rg -n "service_role|SECRET|PRIVATE_KEY|NEXT_PUBLIC|Authorization|auth\\.jwt|raw_user_meta_data|security definer|create policy|storage\\.objects"
npm run build
npm run lint
```

For Supabase, run advisors after policy or schema changes and inspect `pg_policies`, grants, functions, and storage policies with MCP or SQL.