Attack Chain

1. An attacker gains unauthorized access to a user’s valid session cookie through methods like XSS, man-in-the-middle attacks, or physical access to the user’s device.
2. The attacker imports the stolen cookie into their browser.
3. The attacker authenticates to the SillyTavern application using the imported cookie.
4. The victim, suspecting account compromise, changes their password via the /api/users/change-password endpoint or /api/users/recover-step2 after initiating an account recovery.
5. The SillyTavern application updates the password hash in the database but does not invalidate the existing session cookie.
6. The attacker, still possessing the valid cookie, continues to access the victim’s account and perform privileged actions.
7. The attacker views sensitive information, modifies user settings, or interacts with the AI chatbot as the compromised user.
8. The attacker maintains unauthorized access until the cookie expires, by default after 400 days.

Impact

Successful exploitation allows attackers who have stolen session cookies to maintain persistent control over user accounts. Even after a password reset, attackers can continue accessing sensitive information, impersonate the user, and perform unauthorized actions. With a default cookie lifespan of 400 days, this vulnerability presents a significant risk of long-term account compromise, especially in environments where users may be slow to update their passwords or revoke sessions.

Recommendation

• Upgrade SillyTavern installations to version 1.18.0 or later to address the session invalidation vulnerability.
• Enable web server logging and deploy the “Detect SillyTavern Session Cookie Use After Password Change” Sigma rule to identify suspicious activity associated with session reuse.
• Implement strict cookie security policies, including setting the HttpOnly and Secure flags, to reduce the risk of session cookie theft.