# CVE-2026-82021: Hermes Agent 0.18.2 < 0.19.0 MCP Catalog Supply Chain RCE via Mutable Branch Reference

> Remote attackers can execute arbitrary code on hosts installing the Hermes Agent MCP catalog by compromising an upstream repository referenced via a mutable branch.

- **Severity:** Critical 9.0 (`CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 28 Aug 2026
- **Updated:** 31 Aug 2026
- **Also known as:** GHSA-w9gw-vgmg-q67h

## What is CVE-2026-82021?

CVE-2026-82021 is a critical vulnerability in NousResearch hermes-agent, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Hermes Agent 0.18.2 prior to 0.19.0 contains a supply chain vulnerability in its bundled MCP catalog that allows a remote attacker to execute arbitrary code by compromising a third-party upstream repository referenced via a mutable branch rather than a pinned commit SHA. An attacker who compromises the upstream repository can propagate malicious code to every host that installs the affected catalog entry, with no further action required by the operator.

Weakness: CWE-494 (Download of Code Without Integrity Check)

## Which versions are affected by CVE-2026-82021?


## How do I fix CVE-2026-82021?

No fix has been published for CVE-2026-82021 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-82021 being exploited?

There is no known exploitation of CVE-2026-82021 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-82021 and fix it if it is affected.

What it is: CVE-2026-82021 is a critical vulnerability in NousResearch hermes-agent, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-82021 in the wild and no public exploit code.

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-2026-82021/ (Markdown: https://insights.sbomify.com/CVE-2026-82021/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-82021
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-82021
- OSV: https://osv.dev/vulnerability/CVE-2026-82021

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-82021/
Summaries are generated and may contain mistakes; the official description above is the record.