CVE-2026-52869

See a problem?
Please try reporting it to the source first.
Source
https://cve.org/CVERecord?id=CVE-2026-52869
Import Source
https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-52869.json
JSON Data
https://api.osv.dev/v1/vulns/CVE-2026-52869
Aliases
Downstream
Related
Published
2026-07-15T20:06:23.604Z
Modified
2026-07-23T15:11:29.023312800Z
Severity
  • 7.1 (High) CVSS_V3 - CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L CVSS Calculator
Summary
MCP Python SDK: HTTP transports serve session requests without verifying the authenticated principal
Details

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.streamablehttpmanager.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.

Database specific 
{
    "cwe_ids": [
        "CWE-639"
    ],
    "cna_assigner": "GitHub_M",
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52869.json"
}
References

Affected packages

Git / github.com/modelcontextprotocol/python-sdk

Affected ranges

Type
GIT
Repo
https://github.com/modelcontextprotocol/python-sdk
Events
Introduced
0 Unknown introduced commit / All previous commits are affected
Fixed
62137874ff26dd74d2fea80ff528a7fd9ca7a5e7
Fixed
1abcca2408a6b50e10ec601181f63f9978705c00
Fixed
ce267b6fc515dc4efc1dc70b6975b16ff0feef0a
Database specific 
{
    "extracted_events": [
        {
            "introduced": "0"
        },
        {
            "fixed": "1.27.2"
        }
    ],
    "cpe": "cpe:2.3:a:lfprojects:mcp_python_sdk:*:*:*:*:*:*:*:*",
    "source": [
        "CPE_RANGE",
        "REFERENCES"
    ]
}

Affected versions

1.*
1.15.0
v1.*
v1.0.0
v1.10.0
v1.10.1
v1.11.0
v1.12.0
v1.12.1
v1.12.2
v1.12.3
v1.12.4
v1.13.0
v1.13.1
v1.14.0
v1.14.1
v1.15.0
v1.16.0
v1.17.0
v1.18.0
v1.19.0
v1.20.0
v1.21.0
v1.21.1
v1.22.0
v1.23.0
v1.23.1
v1.23.2
v1.23.3
v1.24.0
v1.25.0
v1.26.0
v1.27.0
v1.27.1
v1.4.0
v1.4.1
v1.5.0
v1.6.0
v1.7.0
v1.8.0
v1.8.1
v1.9.0
v1.9.1
v1.9.2
v1.9.3
v1.9.4

Database specific

source 
"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-52869.json"