CVE-2026-25905 — mcp-run-python
MEDIUMCVE-2026-25905 is a medium-severity (CVSS 5.8) CWE-653 vulnerability in mcp-run-python. The records list no fixed version yet; check the vendor advisory below and apply the mitigations in the meantime.
MCP Run Python has a Sandbox Escape & Server Takeover Vulnerability
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-25905.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
mcp-run-pythonReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
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.
Patches
No Patch Available:
The mcp-run-python project is currently archived and maintainers have indicated it is unlikely to receive a fix.
Recommendation: Users are strongly advised to immediately stop using this package. If functionality is required, users must migrate to a maintained alternative that implements proper sandboxing (e.g., running Python in a Docker container or a restricted WASM environment with the JS bridge disabled).
Workarounds
There are no configuration-based workarounds. Securing the environment requires modifying the source code to disable the Pyodide-to-JS bridge or moving the execution environment to a fully isolated sandbox (e.g., a separate container).
Resources
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | mcp-run-python | all versions | No fix |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mcp-run-python, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Remediation status
The records we use list no patched version of mcp-run-python for CVE-2026-25905. Check the maintainer's advisory, and where your build allows, override or pin the dependency away from the vulnerable range.
Mitigate without a patch
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2026-25905 in your dependencies?
Find it across PyPI, including transitive dependencies.