The vulnerability exists in Quivr's chat-related API endpoints due to missing ownership validation on GET, DELETE, and POST operations. This allows an authenticated user to read, delete, or inject messages into any user's chat, exposing private content and tampering with chat histories. The weakness is an authorization bypass represented by CWE‑639. Because the attacker must already be authenticated, the threat is primarily internal but can be leveraged by compromised or malicious accounts.

The affected product is QuivrHQ's quivr application, with all releases up to and including version 0.0.322 vulnerable. Users of quivr 0.0.322 or earlier should consider them at risk until a fix is deployed. No specific vendor patch details were provided in the description, but updating the application to a later version is required.

The CVSS score is 8.6, indicating a high severity. The EPSS score is unavailable and it is not listed in KEV, implying no known widespread exploitation yet. However, because the vulnerability requires an authenticated user, it can be abused by insiders or attackers who gain credentials. The attack path is straightforward: an attacker logs in, issues a GET /chat/{id}/history or similar, and obtains another user's data. The high CVSS combined with the potential for data theft and integrity compromise means the risk is significant.