# Temporary data caches cleared when user logs out or uninstalls

- **Pattern:** `ab-001317` (`extension-data-privacy.third-party-sharing.cache-cleanup`)
- **Severity:** low
- **Lifecycle:** active
- **Last modified:** 2026-04-18
- **Canonical URL:** https://auditbuffet.com/patterns/ab-001317
- **License:** CC-BY-4.0 — attribute to AuditBuffet Pattern Catalog (https://auditbuffet.com/patterns/ab-001317)

## Why it matters

GDPR Art. 5(1)(e) requires personal data not be retained longer than necessary — cached session data that survives a logout or uninstall violates this principle. A user who logs out of an extension expecting their session to be cleared can still have their data re-accessed if the extension is re-opened without re-authentication. GDPR Art. 17 (right to erasure) is practically impossible to honor if cached data persists beyond logout. CWE-212 (Improper Removal of Sensitive Information Before Storage or Transfer) covers this failure. Uninstall handlers that do not clear extension storage leave personal data on the user's device indefinitely — often forgotten and never cleaned up.

## Severity rationale

Low because data persistence after logout is a latent privacy risk rather than an immediate exfiltration — but it directly violates GDPR Art. 5(1)(e) storage limitation and makes Art. 17 erasure requests unenforceable.

## Remediation

Implement a `logout()` function that clears all session state, and hook it to the extension's uninstall event:

```js
function logout() {
  // Clear in-memory state
  currentUser = null;
  sessionCache = {};

  // Clear extension storage keys written during the session
  chrome.storage.local.remove(['authToken', 'sessionId', 'cachedProfile']);
}

// Clear on uninstall — chrome.runtime.setUninstallURL can trigger server-side cleanup
// For local cleanup, use onSuspend in MV2 or alarm-based cleanup in MV3
chrome.storage.local.get(null, (items) => {
  const sessionKeys = Object.keys(items).filter(k => k.startsWith('session_'));
  chrome.storage.local.remove(sessionKeys);
});
```

Document which storage keys are session-scoped vs. persistent preferences, and ensure `logout()` targets only session keys to avoid destroying legitimate user settings on re-install.

## Detection

- **ID:** `cache-cleanup`
- **Severity:** `low`
- **What to look for:** Examine the logout flow and uninstall handlers. Check whether temporary caches (in-memory state, `sessionStorage`, temporary `IndexedDB` tables, or `chrome.storage.local` session data) are cleared when the user logs out or the extension is uninstalled.
- **Pass criteria:** Count all storage keys written during a session. Logout must clear at least 100% of session-specific keys (in-memory caches and session storage). Uninstall handler clears all temporary data (optional: can keep preferences if user reinstalls, but session data should be cleared).
- **Fail criteria:** Logout does not clear cached data. Cache entries persist after logout and can be re-accessed. Uninstall does not trigger cleanup.
- **Skip (N/A) when:** The extension has no logout flow (no user accounts), or no temporary caches are maintained.
- **Detail on fail:** Example: `"User logs out but authToken remains in chrome.storage.local, accessible if extension is used again"` or `"In-memory cache of user profile is not cleared on logout; private data persists."`
- **Remediation:** Clear caches on logout and uninstall:

  ```js
  function logout() {
    // Clear memory
    currentUser = null;
    sessionCache = {};

    // Clear temporary storage
    chrome.storage.local.remove(['authToken', 'sessionId']);

    // Clear IndexedDB temp tables if needed
    indexedDB.deleteDatabase('tempData');
  }

  chrome.runtime.onInstalled.addListener(({ reason }) => {
    if (reason === 'chrome_update') return;
    // Optional: clear all data on uninstall
    chrome.storage.local.clear();
  });
  ```

## External references

- gdpr Art. 5(1)(e)
- gdpr Art. 17
- cwe CWE-212

Taxons: data-integrity, privacy-consent

HTML version: https://auditbuffet.com/patterns/ab-001317