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.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
High
Difficult to exploit
Privileges Required
Low
Basic privileges needed
User Interaction
None
No user interaction needed
Impact Assessment
Confidentiality
High
Complete data leak
Integrity
High
Complete data modification
Availability
Low
Partial disruption
CVSS Vector v3.1
Weakness Type (CWE)
Vulnerable Products 1
| Configuration | From (including) | Up to (excluding) |
|---|---|---|
|
Lfprojects Mcp_Python_Sdk
cpe:2.3:a:lfprojects:mcp_python_sdk:*:*:*:*:*:*:*:*
|
— |
1.27.2
|
References 6
https://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec6…
security-advisories@github.com
https://github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc…
security-advisories@github.com
https://github.com/modelcontextprotocol/python-sdk/pull/2690
security-advisories@github.com
https://github.com/modelcontextprotocol/python-sdk/pull/2719
security-advisories@github.com
https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2
security-advisories@github.com
https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw…
security-advisories@github.com