MCP Run Python has a Sandbox Escape & Server Takeover Vulnerability

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.8 · CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:L

EPSS

• CVE-2026-25905: 0.21% estimated exploitation activity in the next 30 days; percentile 10.80 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact Critical Sandbox Escape & Server Takeover: A critical security vulnerability exists in mcp-run-python due to a lack of isolation between the Python runtime (Pyodide) and the host JavaScript environment. The runPython and runPythonAsync functions execute Python code using Pyodide without restricting access to the JavaScript bridge. This allows any executed Python code—whether from a user or an AI model—to access the js module in Pyodide. Through this bridge, the Python code can modify the global JavaScript environment, interact with the Node.js process, and alter the behavior of the MCP server. Specific Attack Vector: MCP Tool Shadowing Because the Python code can modify the JS runtime, an attacker can dynamically overwrite or "shadow" existing MCP tools registered on the server. For example, an attacker could replace a secure file-reading tool with a malicious version that exfiltrates data to an external server, all while the MCP server appears to be functioning normally.…

Published by the source

9 Feb 2026, 09:30 UTC

Last modified by the source

13 Jul 2026, 16:43 UTC

Source last checked

26 Oct 2026, 13:36 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-pfv4-wmph-5gc6

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-pfv4-wmph-5gc6

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# Patch Next advisory brief: CVE-2026-25905

Advisory: MCP Run Python has a Sandbox Escape & Server Takeover Vulnerability
IDs: CVE-2026-25905, GHSA-pfv4-wmph-5gc6
Record: https://patchnext.com/advisories/cve-2026-25905 (revision 2, source checked 26 Oct 2026, 13:36 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI mcp-run-python: affected <= 0.0.22

## Suggested inspection (read-only)
- `python -m pip show mcp-run-python`: prints the installed version. Run with the environment that serves production active.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on mcp-run-python.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-pfv4-wmph-5gc6 (OSV record GHSA-pfv4-wmph-5gc6 lists affected ranges: PyPI mcp-run-python >=0 <=0.0.22)
- Verified: https://github.com/advisories/GHSA-pfv4-wmph-5gc6 (GitHub-reviewed advisory GHSA-pfv4-wmph-5gc6 lists affected ranges: PyPI mcp-run-python >=0 <=0.0.22)

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