vulntracker.iovulntracker.io
© 2026 vulntracker.io

CVE-2026-52869

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

HIGH
7.1
CVSS Score
Published: July 15, 2026 at 08:06 PM UTC
Updated: October 24, 2026 at 09:10 PM UTC
2 products affected across 2 vendorsMcp Python SDKMcp Python SDK

Using python-sdk by modelcontextprotocol?

Get instant alerts when new vulnerabilities affect python-sdk - before attackers find them.

Real-time alertsTrack your software stackFree plan available
Start FreeSign In
Severity
HIGH7.1
Exploit prediction
EPSS 0.5%
SSVC
No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Mcp Python SDK· Lfprojects
95%
v < 1.27.2
Affected range stops below 1.27.2, so it looks safe — our inference, not a vendor statement
Mcp Python SDK· Modelcontextprotocol
90%
v < 1.27.2
Affected range stops below 1.27.2, so it looks safe — our inference, not a vendor statement

References (6)

x_refsource_CONFIRMVendor Advisory
Source: cverecord
https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58
x_refsource_MISCIssue TrackingPatch
Source: cverecord
https://github.com/modelcontextprotocol/python-sdk/pull/2690
x_refsource_MISCIssue TrackingPatch
Source: cverecord
https://github.com/modelcontextprotocol/python-sdk/pull/2719
x_refsource_MISCPatch
Source: cverecord
https://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00
x_refsource_MISCPatch
Source: cverecord
https://github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0a
x_refsource_MISCRelease Notes
Source: cverecord
https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2

SSVC — Action Prioritization

SSVCNo known exploitNot automatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

7.1HIGHGitHub_M
Attack Vector
NETWORK
Complexity
HIGH
Privileges
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
LOW
Vector?

Quick Info

StatusANALYZED
CWE
CWE-639

Get alerted

Stop reading CVE feeds looking for your own stack

Track the products you run and VulnTracker tells you when a new CVE affects them — with what is known about fixing it, and nothing about the rest.

Create accountSign in
Free plan, no card