CVE-2026-84289 NousResearch hermes-agent MCP Tool mcp_tool.py list_tools memory allocation
Remote attackers can cause denial of service in NousResearch hermes-agent via uncontrolled memory allocation in the MCP tool list function.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-84289?
CVE-2026-84289 is a medium-severity denial of service vulnerability in NousResearch hermes-agent, published on 1 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-84289?
How do I fix CVE-2026-84289?
No fix has been published for CVE-2026-84289 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-84289 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-84289 exists.
Sources
Also known as GHSA-mqg2-c725-2vx3.