Severity: Critical
CVSS Score: 9.1
**Overview** Session cookies of applications using the Auth0 symfony SDK configured with CookieStore have authentication tags that can be brute forced, which may result in unauthorized access. **Am I Affected?** You are affected by this vulnerability if you meet the following pre-conditions: 1. Applications using the Auth0 symfony SDK with version <=5.3.1 2. Auth0/Symfony SDK uses the Auth0-PHP SDK with version 8.0.0-BETA1 or higher and below 8.14.0. 3. Session storage configured with CookieStore. **Fix** Upgrade Auth0/symfony to v5.4.0. As an additional precautionary measure, we recommend rotating your cookie encryption keys. Note that once updated, any previous session cookies will be rejected. **Acknowledgement** Okta would like to thank Félix Charette for discovering this vulnerability.