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

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-24 · updated 2026-07-23
Weakness: CWE-74

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.

Affected products

NousResearch hermes-agent: 2026.4.0, 2026.4.1, 2026.4.2, 2026.4.3, 2026.4.4, 2026.4.5 (+11)

References

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

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