Executive brief
Chainlit, a framework for building AI applications, contains a security flaw that allows unauthorized individuals to take over active user sessions. By providing a valid session ID, an attacker can bypass ownership checks and gain the same permissions as a legitimate user. This could lead to the unauthorized access of sensitive data or the execution of tools and actions on behalf of the victim.
Technical details
A session hijacking vulnerability exists in Chainlit's WebSocket session restoration mechanism. The 'restore_existing_session' path failed to verify if the authenticated user requesting a session restoration actually owned the session associated with the provided 'sessionId'. An attacker who obtains a valid session ID can exploit this lack of authorization (CWE-862) to assume the victim's roles and permissions. This allows for unauthorized tool invocation and access to restricted data. The issue is mitigated in version 2.10.1 by implementing the '_session_owner_matches_user' check during the WebSocket rebind process.
Affected products
- Chainlit Chainlit < 2.10.1
Timeline
- 2026-03-24: patched: Fix merged via Pull Request #2857
- 2026-03-27: advisory: Release 2.10.1 published
- 2026-06-22: disclosed: CVE-2026-56104 published to NVD