# 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.

- **Severity:** Medium 5.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 1 Sep 2026
- **Updated:** 2 Sep 2026
- **Also known as:** GHSA-mqg2-c725-2vx3

## 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.

Weakness: CWE-789 (Memory Allocation with Excessive Size Value), CWE-400 (Uncontrolled Resource Consumption)

## 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.

## Is CVE-2026-84289 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-84289 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-84289 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-84289 exists.

Affected product: NousResearch hermes-agent. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-84289/ (Markdown: https://insights.sbomify.com/CVE-2026-84289/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-84289
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-84289
- OSV: https://osv.dev/vulnerability/CVE-2026-84289

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-84289/
Summaries are generated and may contain mistakes; the official description above is the record.