CVE-2026-25905 json
Lack of isolation in mcp-run-python leads to MCP server takeover
published 9mo ago modified 3mo ago also GHSA-pfv4-wmph-5gc6 , PYSEC-2026-2628 , EUVD-2026-6610
- cvss
- 5.8
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.2%
- EPSS 0.2% chance of exploitation in 30 days, percentile 10%
- public exploits
- 0
- none known
Summary
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.
Is CVE-2026-25905 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.
Check with FencerCISA SSVC
- Exploitation
- Proof of concept is public
- Automatable
- no
- Technical impact
- partial
- Assessed
- 9mo ago
Exploit prediction
0.20% chance of exploitation in the next 30 days, higher than 10% of all scored CVEs (FIRST EPSS, 2026-11-09).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 5.8 | CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:L |
| GitHub | 3.1 | 5.8 | CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:L |
| OSV | 3.1 | 5.8 | CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:L |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| pypi | mcp-run-python | <=0.0.22 |
no fix listed |
Classification
- Weakness
-
- CWE-653 Improper Isolation or Compartmentalization
References
-
research.jfrog.com
/vulnerabilities/mcp-run-python-lack-of-isolation-mcp-takeover-jfsa-2026-001653030/
third-party-advisory
-
nvd.nist.gov
/vuln/detail/CVE-2026-25905
advisory
-
github.com
/pydantic/mcp-run-python
package
-
research.jfrog.com
/vulnerabilities/mcp-run-python-lack-of-isolation-mcp-takeover-jfsa-2026-001653030
web
-
pypi.org
/project/mcp-run-python
package
-
github.com
/advisories/GHSA-pfv4-wmph-5gc6
advisory
Sources
- CVE List CVE-2026-25905
- GitHub Advisory GHSA-pfv4-wmph-5gc6
- NVD CVE-2026-25905
- OSV PYSEC-2026-2628
Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.