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

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

• lfprojects mcp python sdkbefore 1.27.2

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

• modelcontextprotocol python-sdk

  • < 1.27.2affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Other highest-scoring records for the same primary product.

• CVE-2026-59950MCP Python SDK: WebSocket server transport does not support Host/Origin validation
  30Monitor
• CVE-2026-52870MCP Python SDK: Experimental task handlers allow any client to access and cancel other clients' tasks
  30Monitor
• CVE-2025-66416DNS Rebinding Protection Disabled by Default in Model Context Protocol Python SDK for Servers Running on Localhost
  30Monitor

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Root cause

The endpoint fetches the record by the ID sent in the request, but never checks whether the record belongs to the requesting user.

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

1const invoice = await Invoice.findById(req.params.id);2res.json(invoice);

1const invoice = await Invoice.findOne({2  id: req.params.id,3  ownerId: req.user.id,4});5if (!invoice) return res.sendStatus(404);6res.json(invoice);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.