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CVE-2026-52869

MCP Python SDK: HTTP transports serve session requests without verifying the authenticated principal

Published: Jul 15, 2026Updated: Jul 17, 2026 Sources: CVE List NVDCWE-639
7.1HIGH
NVD MITRE
EPSS Score
0.3%
Top 75.6%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available
Self-Check
Not available

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.

No summary for this CVE yet.

CVSS Vector Breakdown

AV:NAC:HPR:LUI:NS:UC:HI:HA:L
Exploitability
AV:NAttack Vector
Network
AC:HAttack Complexity
High
PR:LPrivileges Required
Low
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:HConfidentiality
High
I:HIntegrity
High
A:LAvailability
Low
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Weaknesses

CWE-639

Affected Products

modelcontextprotocol
oss-projectaka model context protocol, mcp
python-sdkMixed
AI / ML / ai-agent-tooling
lfprojects
oss-projectaka valkey, model context protocol servers, mcp servers, mlflow
mcp python sdkMixed
AI / ML / notebook-mlops

Exploitability

Official Patch Available
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Attack Graph

Products CVE Techniques Tactics

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MITRE ATT&CK

1 technique
Initial Access
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References

https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58
github.com
https://github.com/modelcontextprotocol/python-sdk/pull/2690
github.com
https://github.com/modelcontextprotocol/python-sdk/pull/2719
github.com
and 3 more references View all →

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