CVE-2026-52869

Severity CVSS v4.0:

Pending analysis

Type:

Unavailable / Other

Publication date:

15/07/2026

Last modified:

16/07/2026

Description

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.

Impact

Vector 3.x

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L CVSS v3.1 Severity and Metrics:

Base Score: 7.10 HIGH
Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L

Attack Vector (AV): Network
Attack Complexity (AC): High
Privileges Required (PR): Low
User Interaction (UI): None
Scope (S): Unchanged
Confidentiality (C): High
Integrity (I): High
Availability (A): Low

Base Score 3.x

7.10

Severity 3.x

HIGH

CVE-2026-52869

Description

Impact

References to Advisories, Solutions, and Tools