CVE-2026-77519 describes a vulnerability in MaxKB (an open-source AI assistant) where the /chat/api/mcp endpoint authenticates ApplicationApiKeys by checking only the secret and active status, but fails to enforce is_permanent and expire_time checks. Consequently, non-permanent application keys that have expired but remain active can be used to initialize the MCP endpoint, list tool metadata, invoke tools, and create durable application chat states. The standard chat API enforces these checks and rejects such keys, but the MCP endpoint does not. This issue affects versions 2.10.2-lts and earlier. No patch or fixed version is available as of the latest review.

An attacker with a previously valid, non-permanent application key that has expired but remains active can bypass expiration controls on the /chat/api/mcp endpoint. This allows unauthorized access to tool metadata, invocation of tools, and creation of persistent chat records. The confidentiality and integrity of application data accessed via the MCP endpoint are impacted. Availability is not affected. The CVSS 3.1 base score is 5.4 (medium severity), reflecting limited impact on confidentiality and integrity with no impact on availability.

No official fix or patch is currently available for this vulnerability. Users should monitor the vendor's advisories for updates. Until a fix is released, avoid using non-permanent application keys that may remain active after expiration or restrict access to the MCP endpoint to trusted users only. Review and implement additional access controls or session management policies as a temporary mitigation.