MCPA-2026-0033
highauth-missingCVSS 7.1
MCP Python SDK HTTP transports serve session requests without verifying the authenticated principal (CVE-2026-52869)
The MCP Python SDK (PyPI: mcp) before 1.27.2: the SSE and Streamable HTTP server transports routed incoming requests to an existing session based only on the session identifier, without verifying that the request was authenticated as the same principal that created the session. Anyone who learned or guessed a session ID could send JSON-RPC messages on that session regardless of bearer token. Fixed in 1.27.2.
Affected packages
| Ecosystem | Package | Affected versions |
|---|---|---|
| pypi | mcp | >= 0, < 1.27.2 |
Identifiers
CVE-2026-52869GHSA-jpw9-pfvf-9f58CWE-639
References
- advisory https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58
- web https://nvd.nist.gov/vuln/detail/CVE-2026-52869
- fix https://github.com/modelcontextprotocol/python-sdk/pull/2690
Timeline
- Published: 2026-07-16