The flaw is in the DELETE /api/messages/:conversationId/:messageId endpoint of the open‑source LibreChat chat application. The validateMessageReq middleware verifies only that the supplied conversationId belongs to the authenticated user, but does not check ownership of the individual message. The code then calls deleteMessages({ messageId }) using solely the messageId as a MongoDB filter, eliminating any user constraint. As a result, an attacker who authenticates and supplies a valid conversationId together with a victim’s messageId can permanently delete that message from another user’s conversation. This unauthorized deletion can occur with any authenticated request, and the data removed is irrecoverable. It is a missing authorization condition flaw (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.