The NousResearch hermes-agent contains a cross-site scripting vulnerability in the MatrixAdapter._markdown_to_html function within gateway/platforms/matrix.py. This flaw allows remote attackers to execute script code by manipulating markdown input that is converted to HTML without proper sanitization. The vulnerability affects versions 2026.5.29.0 through 2026.5.29.2. Although a pull request with a fix exists, it has not yet been merged or officially released. No official patch or remediation is currently available.

Successful exploitation of this vulnerability could allow an attacker to execute arbitrary scripts in the context of the victim's browser, potentially leading to session hijacking, defacement, or other malicious actions. The vulnerability requires low attack complexity and no privileges but does require user interaction. The impact is limited to cross-site scripting without direct code execution or privilege escalation.

No official patch or fix has been released yet; the pull request to fix the issue is awaiting acceptance. Users should monitor the vendor's repository or advisory channels for the official fix. Until then, consider applying any available temporary mitigations such as input sanitization or disabling markdown rendering if feasible. Avoid exposing the vulnerable component to untrusted users where possible.