# Security

Bill Tracker is a self-hosted app that stores financial records, bank connections, and
encryption keys. Security is a first-class concern.

## Reporting a vulnerability

Please report suspected vulnerabilities privately to the maintainer (do not open a public
issue). Include steps to reproduce and impact. We aim to acknowledge within a few days.

## Controls in place

- **Authentication:** bcrypt passwords, hashed + rotating session tokens, optional TOTP 2FA
  and WebAuthn/FIDO2, OIDC. Failed-login tracking + login history.
- **Authorization:** `requireAuth` / `requireUser` / `requireAdmin` on every non-public
  route; all user data is scoped by `user_id` (isolation is covered by tests).
- **CSRF:** double-submit token (`csrfMiddleware`) on all authenticated mutating routes.
- **Rate limiting:** on auth, admin, import/export, backup, and password-change surfaces.
- **Encryption at rest:** AES-256-GCM with HKDF key derivation for stored secrets
  (SimpleFIN token, SMTP/OIDC secrets, login metadata); a non-reversible key fingerprint
  lets operators verify the active key. Set `TOKEN_ENCRYPTION_KEY` in production so the key
  lives outside the database.
- **Transport/headers:** security headers + CSP (`securityHeaders`), Secure/HttpOnly/SameSite
  cookies, opt-in CORS allowlist.
- **Audit:** security-sensitive actions recorded to `audit_log`.
- **Automated in CI:** secret scanning (gitleaks), dependency audit (`npm audit`), lint +
  typecheck + tests on every push.

## Known dependency-audit exceptions (assessed)

`npm audit` reports two HIGH advisories that are **not currently actionable via npm** and are
assessed as follows:

- **nodemailer — `raw` message option file-read/SSRF.** Not exploitable here: the app builds
  messages via the normal API and never passes a user-controlled `raw` option. The npm fix
  requires nodemailer 9 (breaking); deferred until a maintenance window with SMTP re-test.
- **xlsx (SheetJS) — prototype pollution.** Confined to `services/spreadsheetImportService.cts`
  (import only), which parses with `raw: false` behind a 10 MB size cap and content-type
  allowlist. SheetJS publishes fixes only via its own CDN (not npm); migrating to the CDN
  build (or a maintained alternative) is tracked as follow-up.

The CI dependency gate fails on **critical**; highs are reviewed here.

## Operational hardening

- Set `TOKEN_ENCRYPTION_KEY` (outside the DB) in production.
- Run behind HTTPS with `TRUST_PROXY` set appropriately.
- Turn off verbose/debug logging (e.g. `simplefin_debug_logging`) in production.
- Back up `data/db` encrypted; never commit databases or keys (gitignored + gitleaks).
