FKIE_CVE-2026-52869

Vulnerability from fkie_nvd - Published: 2026-07-15 20:17 - Updated: 2026-07-15 20:54
Severity
7.1 (High) - CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L
Summary
The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to 1.27.2, the SSE and stateful Streamable HTTP transports mcp.server.sse.SseServerTransport and mcp.server.streamable_http_manager.StreamableHTTPSessionManager route requests to existing sessions using only the session_id query parameter or Mcp-Session-Id header without verifying the authenticated principal that created the session, allowing a different bearer-token-authenticated client with a known session ID to inject JSON-RPC messages into that session. This issue is fixed in version 1.27.2.
References
security-advisories@github.comhttps://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00
security-advisories@github.comhttps://github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0a
security-advisories@github.comhttps://github.com/modelcontextprotocol/python-sdk/pull/2690
security-advisories@github.comhttps://github.com/modelcontextprotocol/python-sdk/pull/2719
security-advisories@github.comhttps://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2
security-advisories@github.comhttps://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "python-sdk",
          "vendor": "modelcontextprotocol",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 1.27.2"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to 1.27.2, the SSE and stateful Streamable HTTP transports mcp.server.sse.SseServerTransport and mcp.server.streamable_http_manager.StreamableHTTPSessionManager route requests to existing sessions using only the session_id query parameter or Mcp-Session-Id header without verifying the authenticated principal that created the session, allowing a different bearer-token-authenticated client with a known session ID to inject JSON-RPC messages into that session. This issue is fixed in version 1.27.2."
    }
  ],
  "id": "CVE-2026-52869",
  "lastModified": "2026-07-15T20:54:43.733",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "LOW",
          "baseScore": 7.1,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L",
          "version": "3.1"
        },
        "exploitabilityScore": 1.6,
        "impactScore": 5.5,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-07-15T20:17:38.427",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0a"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/modelcontextprotocol/python-sdk/pull/2690"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/modelcontextprotocol/python-sdk/pull/2719"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Undergoing Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-639"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}



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