CVE-2026-44211: Cline Kanban Server has a Cross-Origin WebSocket Hijacking Vulnerability

Synopsis

Cross-origin WebSocket hijacking vulnerability in Cline Kanban Server (versions 2.13.0 and prior) is reachable over the network without authentication, but requires the victim to visit a malicious page. A successful exploit gives an attacker full control over the WebSocket session, enabling them to read sensitive data, tamper with in-flight messages, and disrupt service. HarborGuard is tracking this advisory and will make a patched-image rebuild available as soon as an upstream fix is published.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityRequired

  The attacker must be able to reach the Cline Kanban Server over the network, making any publicly or internally exposed instance a viable target.

• AuthenticationNot required

  No credentials or prior account access are needed to initiate the WebSocket hijack attempt.

• Victim interactionRequired

  The attack requires a user with an active session to visit an attacker-controlled page, which then hijacks the cross-origin WebSocket connection.

• Attack complexityDetail

  The exploit is reliable and imposes no special environmental conditions or race-condition requirements.

Blast Radius

• A successful attacker reads all data transiting the WebSocket session, including task state, code context, and any credentials or tokens exchanged with the Cline agent.
• The attacker can inject or modify messages over the hijacked connection, altering agent instructions and corrupting in-progress coding tasks.
• The attacker can terminate or disrupt the WebSocket session, crashing the Cline Kanban workflow and causing loss of in-flight task state.
• Because the scope is changed (S:C in the CVSS vector), impact can extend beyond the Cline process itself to other resources accessible via the agent's execution context.