CVE-2026-9354 Details
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.
A vulnerability exists in NousResearch Hermes-Agent versions through 2026.4.16, specifically within the Slack and Mattermost adapters. This issue involves an output sanitization bypass that allows an attacker to manipulate the agent into sending unescaped mass mentions, such as `<!everyone>` or `@all`, directly to external chat platforms. The vulnerability can be exploited remotely, leading to a denial-of-service condition by causing notification exhaustion for all users in a workspace.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed May 24, 2026CISA-ADP
Assessed May 27, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://gist.github.com/YLChen-007/e90fb38ac03284176bae49898a3a46a4 | [email protected] | ExploitTechnical Description |
| https://vuldb.com/submit/812226 | [email protected] | Permission Required |
| https://vuldb.com/vuln/365317 | [email protected] | AdvisoryPermission Required |
| https://vuldb.com/vuln/365317/cti | [email protected] | AdvisoryPermission Required |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-116 | Improper Encoding or Escaping of Output | [email protected] |
| CWE-74 | Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection') | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| NousResearch hermes-agent | <= 2026.4.16 (semver) |
CPE
Remediation
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Change History
4 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 23, 2026 | CVE Translated | [email protected] |
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| May 24, 2026 | New CVE Received | [email protected] |