CVEs / CVE-2026-52869
CVE-2026-52869
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 products · 1
| Product | Versions affected | Fixed in |
|---|---|---|
| lfprojects: mcp python sdk | < 1.27.2 | 1.27.2 |
Versions as NVD's CPE configuration states them; "—" means the record gives no fixed version, not that none exists. Check the vendor's advisory in the references.
In this registry
- python-sdk — agent dossier
- typescript-sdk — agent dossier
References · 6
- github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00 — Patch
- github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0a — Patch
- github.com/modelcontextprotocol/python-sdk/pull/2690 — Issue Tracking, Patch
- github.com/modelcontextprotocol/python-sdk/pull/2719 — Issue Tracking, Patch
- github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2 — Release Notes
- github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58 — Vendor Advisory
The official record's references, as NVD lists them, minus any tagged Exploit. Nothing here is an exploit or a proof of concept.
Description, scores, versions and references are the official CVE record's own, retrieved 2026-10-26 from NVD. Category, attack surface and cross-links are this registry's classification and can be wrong — use the button above. Not a severity assessment for your deployment.