# CVE-2026-25905: Lack of isolation in mcp-run-python leads to MCP server takeover

> Attackers can execute arbitrary code to hijack the MCP server due to lack of isolation between Python and JavaScript environments in the archived mcp-run-python library.

- **Severity:** Medium 5.8 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:L`)
- **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:** 9 Feb 2026
- **Updated:** 9 Feb 2026
- **Also known as:** GHSA-pfv4-wmph-5gc6, PYSEC-2026-2628

## What is CVE-2026-25905?

CVE-2026-25905 is a medium-severity code injection vulnerability in mcp-run-python, published on 9 Feb 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

The Python code being run by 'runPython' or 'runPythonAsync' is not isolated from the rest of the JS code, allowing any Python code to use the Pyodide APIs to modify the JS environment. This may result in an attacker hijacking the MCP server - for malicious purposes including MCP tool shadowing. Note - the "mcp-run-python" project is archived and unlikely to receive a fix.

Weakness: CWE-653 (Improper Isolation or Compartmentalization)

## Which versions are affected by CVE-2026-25905?

3 open source packages ship an affected version, including mcp-run-python.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `mcp-run-python` | PyPI | All versions to 0.0.22 | None |
| `mcp-run-python` | PyPI | All versions to 0.0.22 | None |
| `mcp-run-python` | PyPI | All versions to 0.0.22 | None |

## How do I fix CVE-2026-25905?

No fix has been published for CVE-2026-25905 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-25905 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-25905 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-25905 and fix it if it is affected.

What it is: CVE-2026-25905 is a medium-severity code injection vulnerability in mcp-run-python, published on 9 Feb 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: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-25905 exists.

Affected packages and fixed versions:
- mcp-run-python (PyPI): affected all versions up to 0.0.22; no fix listed
- mcp-run-python (PyPI): affected all versions up to 0.0.22; no fix listed
- mcp-run-python (PyPI): affected all versions up to 0.0.22; no fix listed

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-2026-25905/ (Markdown: https://insights.sbomify.com/CVE-2026-25905/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-25905
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-25905
- OSV: https://osv.dev/vulnerability/CVE-2026-25905

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-25905/
Summaries are generated and may contain mistakes; the official description above is the record.