MCP Python SDK: HTTP transports serve session requests without verifying the authenticated principal
Published Jul 15, 2026
7.1
HIGHCVSS 3.1
EPSS 0.53%
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.
Affected products
-
- Version < 1.27.2StatusaffectedConstraints-
- Version
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Modelcontextprotocol | Python-Sdk | n/a |
|
- < 1.27.2
No data.
No Red Hat product state for this CVE.
No package ranges for this CVE.
Remediation
No remediation recorded yet.
References (9)
- https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-44795 Advisory
- https://github.com/advisories/GHSA-jpw9-pfvf-9f58 Advisory
- https://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00 x_refsource_MISCPatch
- https://github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0a x_refsource_MISCPatch
- https://github.com/modelcontextprotocol/python-sdk/pull/2690 x_refsource_MISCIssue TrackingPatch
- https://github.com/modelcontextprotocol/python-sdk/pull/2719 x_refsource_MISCIssue TrackingPatch
- https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2 x_refsource_MISCRelease Notes
- https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58 x_refsource_CONFIRMVendor Advisory
- https://nvd.nist.gov/vuln/detail/CVE-2026-52869
| Link | Providers | Tags |
|---|---|---|
| https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-44795 | Advisory | |
| https://github.com/advisories/GHSA-jpw9-pfvf-9f58 | Advisory | |
| https://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00 | x_refsource_MISCPatch | |
| https://github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0a | x_refsource_MISCPatch | |
| https://github.com/modelcontextprotocol/python-sdk/pull/2690 | x_refsource_MISCIssue TrackingPatch | |
| https://github.com/modelcontextprotocol/python-sdk/pull/2719 | x_refsource_MISCIssue TrackingPatch | |
| https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2 | x_refsource_MISCRelease Notes | |
| https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58 | x_refsource_CONFIRMVendor Advisory | |
| https://nvd.nist.gov/vuln/detail/CVE-2026-52869 |
Change history (0)
No recorded changes yet.