Vulnerability-Lookup

CVE-2026-25905 (GCVE-0-2026-25905)

Vulnerability from cvelistv5 – Published: 2026-02-09 09:01 – Updated: 2026-02-09 12:55

Title

Lack of isolation in mcp-run-python leads to MCP server takeover

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.

Severity ?

5.8 (Medium)


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

CWE

CWE-653 - Improper Isolation or Compartmentalization

Assigner

JFROG

References

URL

Tags

https://research.jfrog.com/vulnerabilities/mcp-ru…

third-party-advisory

Impacted products

	Vendor	Product	Version
			Affected: 0 (python)

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-25905

Vulnerability from fkie_nvd - Published: 2026-02-09 09:16 - Updated: 2026-02-09 16:08

Severity ?

5.8 (Medium) - CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:L

Summary

References

	URL	Tags
	reefs@jfrog.com	https://research.jfrog.com/vulnerabilities/mcp-run-python-lack-of-isolation-mcp-takeover-jfsa-2026-001653030/

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "The Python code being run by \u0027runPython\u0027 or \u0027runPythonAsync\u0027 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."
    },
    {
      "lang": "es",
      "value": "El c\u00f3digo Python ejecutado por \u0027runPython\u0027 o \u0027runPythonAsync\u0027 no est\u00e1 aislado del resto del c\u00f3digo JS, permitiendo que cualquier c\u00f3digo Python utilice las API de Pyodide para modificar el entorno JS. Esto puede resultar en que un atacante secuestre el servidor MCP - con fines maliciosos, incluida la suplantaci\u00f3n de herramientas MCP. Nota - el proyecto \"mcp-run-python\" est\u00e1 archivado y es poco probable que reciba una soluci\u00f3n."
    }
  ],
  "id": "CVE-2026-25905",
  "lastModified": "2026-02-09T16:08:35.290",
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          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "LOW",
          "integrityImpact": "LOW",
          "privilegesRequired": "NONE",
          "scope": "CHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:L",
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        "exploitabilityScore": 1.6,
        "impactScore": 3.7,
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  "published": "2026-02-09T09:16:34.030",
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GHSA-PFV4-WMPH-5GC6

Vulnerability from github – Published: 2026-02-09 09:30 – Updated: 2026-02-12 03:09

Summary

MCP Run Python has a Sandbox Escape & Server Takeover Vulnerability

Details

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

Severity ?

5.8 (Medium)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "mcp-run-python"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "0.0.22"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-25905"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-653"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-02-12T03:09:38Z",
    "nvd_published_at": "2026-02-09T09:16:34Z",
    "severity": "MODERATE"
  },
  "details": "### Impact\n**Critical Sandbox Escape \u0026 Server Takeover:**\nA critical security vulnerability exists in `mcp-run-python` due to a lack of isolation between the Python runtime (Pyodide) and the host JavaScript environment.\n\nThe `runPython` and `runPythonAsync` functions execute Python code using Pyodide without restricting access to the JavaScript bridge. This allows any executed Python code\u2014whether from a user or an AI model\u2014to 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.\n\n**Specific Attack Vector: MCP Tool Shadowing**\nBecause 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.\n\n### Patches\n**No Patch Available:**\nThe `mcp-run-python` project is currently **archived** and maintainers have indicated it is unlikely to receive a fix.\n\n**Recommendation:**\nUsers are strongly advised to **immediately stop using** this package.\nIf 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).\n\n### Workarounds\nThere 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).\n\n### Resources\n* [CVE-2026-25905](https://nvd.nist.gov/vuln/detail/CVE-2026-25905)\n* [JFrog Security Analysis: MCP Takeover](https://research.jfrog.com/vulnerabilities/mcp-run-python-lack-of-isolation-mcp-takeover-jfsa-2026-001653030)",
  "id": "GHSA-pfv4-wmph-5gc6",
  "modified": "2026-02-12T03:09:38Z",
  "published": "2026-02-09T09:30:22Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-25905"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/pydantic/mcp-run-python"
    },
    {
      "type": "WEB",
      "url": "https://research.jfrog.com/vulnerabilities/mcp-run-python-lack-of-isolation-mcp-takeover-jfsa-2026-001653030"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "MCP Run Python has a Sandbox Escape \u0026 Server Takeover Vulnerability"
}

Sightings

Author	Source	Type	Date

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

CVE-2026-25905 (GCVE-0-2026-25905)

FKIE_CVE-2026-25905

GHSA-PFV4-WMPH-5GC6

Impact

Patches

Workarounds

Resources

Tags

Sightings

Nomenclature