The vulnerability exists in the DELETE /api/messages/:conversationId/:messageId endpoint of LibreChat, where an authenticated user can delete any message from another user’s conversation. The handler performs only conversationId validation but then deletes by messageId alone, allowing an attacker to supply a victim’s messageId after passing ownership checks. Removing a message is permanent and results in loss of data, posing confidentiality risk due to unauthorized data removal. This flaw is a missing authorization weakness (CWE‑862).

This issue affects all installations of LibreChat prior to version 0.8.4‑rc1. The exposed endpoint is available to authenticated users of the open-source application, making all users potential targets. The configuration defaults to allowing any authenticated request to reach the deleteMessages route without further permission checks. Updating to 0.8.4‑rc1 or applying the vendor’s patch resolves the problem.

The CVSS score of 5.3 classifies the flaw as medium severity, but the absence of an EPSS score makes the exploitation probability unclear. It is not listed in CISA’s KEV catalog, so no active exploits are publicly known. If an attacker gains access to a user’s credentials, the lack of authorization in the deleteMessages route enables direct exploitation via a standard HTTP request.