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CVE-2026-52869

HIGH
7.1
CVSS 3.1
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.

Metadata

CVE ID
CVE-2026-52869
State
PUBLISHED
Assigner
GitHub_M
Reserved
2026-06-08 21:44 UTC
Published
2026-07-15 20:06 UTC
Last updated
2026-07-15 20:06 UTC
Primary CWE
CWE-639
CWE-639: Authorization Bypass Through User-Controlled Key
Vendor / Product
modelcontextprotocol / python-sdk
Sources
cve.org  ·  NVD

Severity & Metrics

7.1 HIGH CVSS 3.1
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L
Affected products (1)
VendorProductPlatformVersions
modelcontextprotocol python-sdk — < 1.27.2
Weakness (CWE)
CWESourceDescription
CWE-639 cna CWE-639: Authorization Bypass Through User-Controlled Key
CVSS scores (1)
ScoreSeverityVersionSourceVector
7.1 HIGH 3.1 cna CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L
References (6)
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