Summary
MCP Run Python has a Sandbox Escape & Server Takeover Vulnerability
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
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.
CVE-2026-25905 has a CVSS score of 5.8 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
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).
Frequently Asked Questions
- What is CVE-2026-25905? CVE-2026-25905 is a medium-severity security vulnerability in mcp-run-python (pip), affecting versions <= 0.0.22. No fixed version is listed yet.
- How severe is CVE-2026-25905? CVE-2026-25905 has a CVSS score of 5.8 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of mcp-run-python are affected by CVE-2026-25905? mcp-run-python (pip) versions <= 0.0.22 is affected.
- Is there a fix for CVE-2026-25905? No fixed version is listed for CVE-2026-25905 yet. Monitor the advisory for updates and apply mitigations in the interim.
- Is CVE-2026-25905 exploitable, and should I be worried? Whether CVE-2026-25905 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-25905 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.