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.
- 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
- None listed
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
Which versions are affected by CVE-2026-25905?
3 open source packages ship an affected version, including mcp-run-python.
| Package | 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.
Upgrade, and never evaluate templates, expressions or code built from user input. More about Code injection.
Is CVE-2026-25905 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-25905 exists.
Sources
Also known as GHSA-pfv4-wmph-5gc6, PYSEC-2026-2628.