Vulnerability-Lookup

PYSEC-2026-1365

Vulnerability from pysec - Published: 2026-07-07 16:03 - Updated: 2026-07-07 17:24

Details

Summary

A command-injection vulnerability lets any attacker who can influence the server_name field of an MCP execute arbitrary OS commands on Windows hosts that run fastmcp install cursor

Details

generate_cursor_deeplink(server_name, …) embeds server_name verbatim in a cursor://…?name= query string.
open_deeplink() is invoked with shell=True only on Windows. That calls cmd.exe /c start .
Any cmd metacharacter inside server_name (&, |, >, ^, …) escapes the start command and spawns an attacker-chosen process.

PoC

server.py


import random
from fastmcp import FastMCP

mcp = FastMCP(name="test&calc")

@mcp.tool
def roll_dice(n_dice: int) -> list[int]:
    """Roll `n_dice` 6-sided dice and return the results."""
    return [random.randint(1, 6) for _ in range(n_dice)]

if __name__ == "__main__":
    mcp.run()

then run in the terminal: fastmcp install cursor server.py

Impact

OS Command / Shell Injection (CWE-78) Every Windows host that runs fastmcp install cursor is at risk. Developers on their local workstations, CI/CD agents and corporate build machines alike.

Severity

5.4 (Medium)


                  
                    CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Impacted products

Name	purl
fastmcp	pkg:pypi/fastmcp

Aliases

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "fastmcp",
        "purl": "pkg:pypi/fastmcp"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.13.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.1.0",
        "0.2.0",
        "0.3.0",
        "0.3.1",
        "0.3.2",
        "0.3.3",
        "0.3.4",
        "0.3.5",
        "0.4.0",
        "0.4.1",
        "1.0",
        "2.0.0",
        "2.1.0",
        "2.1.1",
        "2.1.2",
        "2.10.0",
        "2.10.1",
        "2.10.2",
        "2.10.3",
        "2.10.4",
        "2.10.5",
        "2.10.6",
        "2.11.0",
        "2.11.1",
        "2.11.2",
        "2.11.3",
        "2.12.0",
        "2.12.0rc1",
        "2.12.1",
        "2.12.2",
        "2.12.3",
        "2.12.4",
        "2.12.5",
        "2.13.0rc1",
        "2.13.0rc2",
        "2.13.0rc3",
        "2.2.0",
        "2.2.1",
        "2.2.10",
        "2.2.2",
        "2.2.3",
        "2.2.4",
        "2.2.5",
        "2.2.6",
        "2.2.7",
        "2.2.8",
        "2.2.9",
        "2.3.0",
        "2.3.0rc1",
        "2.3.1",
        "2.3.2",
        "2.3.3",
        "2.3.4",
        "2.3.5",
        "2.4.0",
        "2.5.0",
        "2.5.1",
        "2.5.2",
        "2.6.0",
        "2.6.1",
        "2.7.0",
        "2.7.1",
        "2.8.0",
        "2.8.1",
        "2.9.0",
        "2.9.1",
        "2.9.2"
      ]
    }
  ],
  "aliases": [
    "CVE-2025-62801",
    "GHSA-rj5c-58rq-j5g5"
  ],
  "details": "### Summary\nA command-injection vulnerability lets any attacker who can influence the server_name field of an MCP execute arbitrary OS commands on Windows hosts that run fastmcp install cursor\n\n### Details\n1. generate_cursor_deeplink(server_name, \u2026) embeds server_name verbatim in a cursor://\u2026?name= query string.\n2. open_deeplink() is invoked with shell=True only on Windows. That calls cmd.exe /c start \u003cdeeplink\u003e.\n3. Any cmd metacharacter inside server_name (\u0026, |, \u003e, ^, \u2026) escapes the start command and spawns an attacker-chosen process.\n\n### PoC\nserver.py \n```\n\nimport random\nfrom fastmcp import FastMCP\n\nmcp = FastMCP(name=\"test\u0026calc\")\n\n@mcp.tool\ndef roll_dice(n_dice: int) -\u003e list[int]:\n    \"\"\"Roll `n_dice` 6-sided dice and return the results.\"\"\"\n    return [random.randint(1, 6) for _ in range(n_dice)]\n\nif __name__ == \"__main__\":\n    mcp.run()\n```\n\nthen run in the terminal:\n`fastmcp install cursor server.py`\n\n### Impact\nOS Command / Shell Injection (CWE-78)\nEvery Windows host that runs fastmcp install cursor is at risk. Developers on their local workstations, CI/CD agents and corporate build machines alike.",
  "id": "PYSEC-2026-1365",
  "modified": "2026-07-07T17:24:07.868280Z",
  "published": "2026-07-07T16:03:08.659725Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/jlowin/fastmcp/security/advisories/GHSA-rj5c-58rq-j5g5"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-62801"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/jlowin/fastmcp"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/fastmcp"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-rj5c-58rq-j5g5"
    }
  ],
  "severity": [
    {
      "score": "CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "FastMCP vulnerable to windows command injection in FastMCP Cursor installer via server_name"
}

CVE-2025-62801 (GCVE-0-2025-62801)

Vulnerability from cvelistv5 – Published: 2025-10-28 21:36 – Updated: 2025-10-29 14:54

Title

FastMCP vulnerable to windows command injection in FastMCP Cursor installer via server_name

Summary

FastMCP is the standard framework for building MCP applications. Versions prior to 2.13.0, a command-injection vulnerability lets any attacker who can influence the server_name field of an MCP execute arbitrary OS commands on Windows hosts that run fastmcp install cursor. This vulnerability is fixed in 2.13.0.

Severity

5.4 (Medium)


                        
                          CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

SSVC

Exploitation: poc Automatable: no Technical Impact: total

CISA Coordinator (v2.0.3)

CWE

CWE-78 - Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

Assigner

GitHub_M

References

1 reference

URL	Tags
https://github.com/jlowin/fastmcp/security/adviso…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version
jlowin	fastmcp	Affected: < 2.13.0

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2025-62801",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2025-10-29T14:54:52.707678Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2025-10-29T14:54:56.687Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
            ],
            "url": "https://github.com/jlowin/fastmcp/security/advisories/GHSA-rj5c-58rq-j5g5"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "fastmcp",
          "vendor": "jlowin",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 2.13.0"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "FastMCP is the standard framework for building MCP applications. Versions prior to 2.13.0, a command-injection vulnerability lets any attacker who can influence the server_name field of an MCP execute arbitrary OS commands on Windows hosts that run fastmcp install cursor. This vulnerability is fixed in 2.13.0."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "PRESENT",
            "attackVector": "LOCAL",
            "baseScore": 5.4,
            "baseSeverity": "MEDIUM",
            "privilegesRequired": "LOW",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "ACTIVE",
            "vectorString": "CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N",
            "version": "4.0",
            "vulnAvailabilityImpact": "HIGH",
            "vulnConfidentialityImpact": "HIGH",
            "vulnIntegrityImpact": "HIGH"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-78",
              "description": "CWE-78: Improper Neutralization of Special Elements used in an OS Command (\u0027OS Command Injection\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2025-10-28T21:36:41.167Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/jlowin/fastmcp/security/advisories/GHSA-rj5c-58rq-j5g5",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/jlowin/fastmcp/security/advisories/GHSA-rj5c-58rq-j5g5"
        }
      ],
      "source": {
        "advisory": "GHSA-rj5c-58rq-j5g5",
        "discovery": "UNKNOWN"
      },
      "title": "FastMCP vulnerable to windows command injection in FastMCP Cursor installer via server_name"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2025-62801",
    "datePublished": "2025-10-28T21:36:41.167Z",
    "dateReserved": "2025-10-22T18:55:48.012Z",
    "dateUpdated": "2025-10-29T14:54:56.687Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

GHSA-RJ5C-58RQ-J5G5

Vulnerability from github – Published: 2025-10-29 15:39 – Updated: 2025-10-29 15:39

Summary

FastMCP vulnerable to windows command injection in FastMCP Cursor installer via server_name

Details

Summary

A command-injection vulnerability lets any attacker who can influence the server_name field of an MCP execute arbitrary OS commands on Windows hosts that run fastmcp install cursor

Details

generate_cursor_deeplink(server_name, …) embeds server_name verbatim in a cursor://…?name= query string.
open_deeplink() is invoked with shell=True only on Windows. That calls cmd.exe /c start .
Any cmd metacharacter inside server_name (&, |, >, ^, …) escapes the start command and spawns an attacker-chosen process.

PoC

server.py


import random
from fastmcp import FastMCP

mcp = FastMCP(name="test&calc")

@mcp.tool
def roll_dice(n_dice: int) -> list[int]:
    """Roll `n_dice` 6-sided dice and return the results."""
    return [random.randint(1, 6) for _ in range(n_dice)]

if __name__ == "__main__":
    mcp.run()

then run in the terminal: fastmcp install cursor server.py

Impact

OS Command / Shell Injection (CWE-78) Every Windows host that runs fastmcp install cursor is at risk. Developers on their local workstations, CI/CD agents and corporate build machines alike.

Severity

5.4 (Medium)


                  
                    CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "fastmcp"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.13.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2025-62801"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-78"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2025-10-29T15:39:03Z",
    "nvd_published_at": "2025-10-28T22:15:37Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\nA command-injection vulnerability lets any attacker who can influence the server_name field of an MCP execute arbitrary OS commands on Windows hosts that run fastmcp install cursor\n\n### Details\n1. generate_cursor_deeplink(server_name, \u2026) embeds server_name verbatim in a cursor://\u2026?name= query string.\n2. open_deeplink() is invoked with shell=True only on Windows. That calls cmd.exe /c start \u003cdeeplink\u003e.\n3. Any cmd metacharacter inside server_name (\u0026, |, \u003e, ^, \u2026) escapes the start command and spawns an attacker-chosen process.\n\n### PoC\nserver.py \n```\n\nimport random\nfrom fastmcp import FastMCP\n\nmcp = FastMCP(name=\"test\u0026calc\")\n\n@mcp.tool\ndef roll_dice(n_dice: int) -\u003e list[int]:\n    \"\"\"Roll `n_dice` 6-sided dice and return the results.\"\"\"\n    return [random.randint(1, 6) for _ in range(n_dice)]\n\nif __name__ == \"__main__\":\n    mcp.run()\n```\n\nthen run in the terminal:\n`fastmcp install cursor server.py`\n\n### Impact\nOS Command / Shell Injection (CWE-78)\nEvery Windows host that runs fastmcp install cursor is at risk. Developers on their local workstations, CI/CD agents and corporate build machines alike.",
  "id": "GHSA-rj5c-58rq-j5g5",
  "modified": "2025-10-29T15:39:03Z",
  "published": "2025-10-29T15:39:03Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/jlowin/fastmcp/security/advisories/GHSA-rj5c-58rq-j5g5"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-62801"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/jlowin/fastmcp"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "FastMCP vulnerable to windows command injection in FastMCP Cursor installer via server_name"
}

Sightings

Author	Source	Type	Date	Other

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

PYSEC-2026-1365

Summary

Details

PoC

Impact

CVE-2025-62801 (GCVE-0-2025-62801)

GHSA-RJ5C-58RQ-J5G5

Summary

Details

PoC

Impact

Tags

Sightings

Nomenclature