Model Context Protocol Python SDK: HTTP client transports followed cross-origin redirects carrying custom headers and bodies

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-116685
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-27 20:17:13 UTC
Updated2026-10-27 20:17:13 UTC
DescriptionThe Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients. From 1.8.0 until 1.30.0 and 2.2.0, streamable_http_client, streamablehttp_client, sse_client, ClientSessionGroup, OAuth, and create_mcp_http_client client paths enable follow_redirects and follow redirects to a different origin, forwarding caller-supplied custom credential headers and, for 307 or 308 responses, the request body. An attacker who can influence a trusted endpoint's redirect destination can receive that material. This issue is fixed in versions 1.30.0 and 2.2.0.

Risk And Classification

Primary CVSS: v3.1 5.9 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Problem Types: CWE-200 | CWE-200 CWE-200: Exposure of Sensitive Information to an Unauthorized Actor

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary5.9MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
3.1CNADECLARED5.9MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Modelcontextprotocol Python-sdk affected >= 1.8.0, < 1.30.0 Not specified
CNA Modelcontextprotocol Python-sdk affected >= 2.0.0, < 2.2.0 Not specified

References

ReferenceSourceLinkTags
github.com/modelcontextprotocol/python-sdk/pull/3397 [email protected] github.com
github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-5h93... [email protected] github.com
github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0 [email protected] github.com
github.com/modelcontextprotocol/python-sdk/commit/2106335745563b2321b8c7... [email protected] github.com
github.com/modelcontextprotocol/python-sdk/commit/c6762e821c527925f0b617... [email protected] github.com
github.com/modelcontextprotocol/python-sdk/releases/tag/v2.2.0 [email protected] github.com
github.com/modelcontextprotocol/python-sdk/pull/3448 [email protected] github.com
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