CVE-2026-15311 NousResearch hermes-agent Matrix Adapter matrix.py MatrixAdapter._markdown_to_html cross site scripting
Remote attackers can execute arbitrary scripts via the Matrix adapter's markdown conversion, potentially compromising user sessions or data.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-15311?
CVE-2026-15311 is a medium-severity cross-site scripting vulnerability in NousResearch hermes-agent, published on 9 Jul 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
A vulnerability was identified in NousResearch hermes-agent up to 2026.5.29.2. Affected by this issue is the function MatrixAdapter._markdown_to_html of the file gateway/platforms/matrix.py of the component Matrix Adapter. Such manipulation leads to cross site scripting. The attack can be executed remotely. The exploit is publicly available and might be used. The pull request to fix this issue awaits acceptance.
Which versions are affected by CVE-2026-15311?
How do I fix CVE-2026-15311?
No fix has been published for CVE-2026-15311 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-15311 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-15311 exists.
Sources
Also known as GHSA-93m6-38r7-vqmh.