CVE-2026-56104 Chainlit CVE debrief

Who should care

Security teams and administrators responsible for Chainlit installations should be aware of this vulnerability. They should assess their exposure and apply the necessary patches to prevent session hijacking attacks. Additionally, defenders should monitor for suspicious WebSocket session restoration attempts and implement compensating controls to detect and prevent exploitation.

Technical summary

The vulnerability exists in the WebSocket session restoration mechanism of Chainlit. When a user initiates a WebSocket connection, Chainlit allows the restoration of an existing session by presenting a valid sessionId. However, the current implementation does not verify the ownership of the sessionId, allowing an attacker to hijack an authenticated user's session. The attacker can then assume the victim's permissions and roles, enabling unauthorized access to restricted data and tools. The vulnerability is addressed in Chainlit version 2.10.1, which introduces proper ownership verification for session restoration.

Defensive priority

High priority should be given to patching Chainlit installations to version 2.10.1 or later. In addition to patching, defenders should monitor WebSocket session restoration attempts and implement additional security controls to detect and prevent exploitation.

Recommended defensive actions

• Update Chainlit to version 2.10.1 or later
• Monitor WebSocket session restoration attempts for suspicious activity
• Implement compensating controls to detect and prevent session hijacking
• Review and update incident response plans to address potential exploitation
• Conduct a thorough inventory of Chainlit installations and assess exposure

Evidence notes

The CVE-2026-56104 vulnerability is based on information from the official CVE record and NVD detail pages. The vulnerability was disclosed by Vulncheck and has been addressed by Chainlit in version 2.10.1. Additional information can be found in the source references provided.

Official resources