CVE-2026-56104: Chainlit < 2.10.1 Session Hijacking via WebSocket Session Restoration

Synopsis

This is a session hijacking vulnerability in Chainlit, the open-source Python framework for building chat-model interfaces. An unauthenticated attacker who obtains a valid session ID can present it during the WebSocket session restoration handshake and take over the corresponding authenticated user session, because the server does not verify that the requester owns the session. Successful exploitation gives the attacker full access to the victim's permissions, roles, tool invocations, and any data the victim's session can reach. A patched-image rebuild at version 2.10.1 is available on HarborGuard for environments running an affected version.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityRequired

  The attacker must reach the Chainlit WebSocket endpoint over the network; the service must be accessible from the attacker's origin.

• AuthenticationNot required

  No credentials or account are required; the attacker only needs a valid session ID belonging to another user.

• Victim interactionNot required

  The attacker exploits the restore path directly without any action required from the victim at exploit time.

• Attack complexityDetail

  Exploitation requires the attacker to first obtain a valid session ID through a separate means (e.g., network interception or leakage), adding an environmental prerequisite before the hijack step.

Blast Radius

• The attacker reads all data accessible to the hijacked session, including conversation history, tool outputs, and any files or records the victim's role can retrieve.
• The attacker invokes tools and backend actions with the victim's full permissions, allowing creation, modification, or deletion of resources the victim is authorized to change.
• Session continuity for the legitimate victim is disrupted, as the restored session can be consumed or manipulated by the attacker.