Executive brief
Chainlit is a framework for building conversational AI applications. An unauthenticated attacker can exploit improper validation of the socket.io sessionId parameter to manipulate file paths and delete arbitrary directories on the server, potentially causing service disruption or data loss.
Technical details
The vulnerability is a path traversal flaw in Chainlit's socket.io session handling. The application fails to properly validate or sanitize the client-supplied sessionId parameter, allowing attackers to inject absolute or relative path sequences (e.g., "../" or "/etc/"). An unauthenticated attacker can craft malicious sessionId values that escape the intended upload directory and recursively delete arbitrary directories accessible to the service process. No authentication is required; the attack is network-accessible via the socket.io interface.
Affected products
- Chainlit Chainlit through 2.12.0
Timeline
- 2026-09-09: disclosed