Hermes WebUI versions earlier than 0.51.443 suffer from a broken access control flaw in the /api/session endpoint that permits an authenticated user to request session transcripts belonging to another profile. The vulnerability arises from the ability to query any session ID via a GET request, thereby exposing private conversation transcripts and metadata, a violation of confidentiality and privacy commitments. The weakness is categorized as CWE-639, improper authorization controls that allow a party to access resources not intended for them.

The affected product is nesquena Hermes WebUI. All releases earlier than 0.51.443 are vulnerable unless a later fix has been applied. Administrators should verify the installed version and ensure it is at least 0.51.443 or higher.

The CVSS score of 7.1 denotes a medium severity vulnerability, and an EPSS score of less than 1% indicates a very low likelihood of exploitation in the wild. The vulnerability requires that the attacker be authenticated, and the attacker must know or guess a foreign session identifier to exploit it. The attack vector is inferred as authenticated, with the attacker able to bypass profile boundary checks by directly querying the session endpoint. The vulnerability is not listed in the CISA KEV catalog, suggesting no confirmed or widespread exploitation has been reported.