CVE-2026-84289: NousResearch hermes-agent MCP Tool mcp_tool.py list_tools memory allocation

Severity: medium (CVSS 4.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-01 · updated 2026-09-02
Weakness: CWE-400

Description

A vulnerability was found in NousResearch hermes-agent up to 0.18.2. This vulnerability affects the function list_tools of the file tools/mcp_tool.py of the component MCP Tool. Performing a manipulation results in uncontrolled memory allocation. It is possible to initiate the attack remotely. The exploit has been made public and could be used. The vendor was contacted early about this disclosure but did not respond in any way.

Affected products

NousResearch hermes-agent: 0.18.0, 0.18.1, 0.18.2

References

https://github.com/lche511/cve/blob/main/Hermes_MCP_Tool_Resource_Amplification_DoS_Report/REPORT.md
https://vuldb.com/cve/CVE-2026-84289
https://vuldb.com/submit/882960
https://vuldb.com/vuln/397720
https://vuldb.com/vuln/397720/cti

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