CVE-2026-52869
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.
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
mcpPyPI | < 1.27.2 | 1.27.2 |
Affected products
5- Range: <1.27.2
- osv-coords3 versions
< 1.172.0-r1+ 2 more
- (no CPE)range: < 1.172.0-r1
- (no CPE)range: < 1.93.0-r0
- (no CPE)range: < 1.172.0-r1
Patches
Vulnerability mechanics
References
8- github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00nvdPatchWEB
- github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0anvdPatchWEB
- github.com/modelcontextprotocol/python-sdk/pull/2690nvdIssue TrackingPatchWEB
- github.com/modelcontextprotocol/python-sdk/pull/2719nvdIssue TrackingPatchWEB
- github.com/advisories/GHSA-jpw9-pfvf-9f58ghsaADVISORY
- github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58nvdVendor AdvisoryWEB
- nvd.nist.gov/vuln/detail/CVE-2026-52869ghsaADVISORY
- github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2nvdRelease NotesWEB
News mentions
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