CVE-2026-116685

MEDIUM 5.9

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

CVSS Score

5.9

EPSS Score

0.0%

EPSS Percentile

0th

The 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.

CWE	CWE-200
Vendor	modelcontextprotocol
Product	python-sdk
Published	Oct 27, 2026

Stay Ahead of the Next One

Get instant alerts for modelcontextprotocol python-sdk

Be the first to know when new medium vulnerabilities affecting modelcontextprotocol python-sdk are published — delivered to Slack, Telegram or Discord.

Get Free Alerts → Free · No credit card · 60 sec setup

CVSS v3 Breakdown

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

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None

Affected Versions

modelcontextprotocol / python-sdk

>= 1.8.0, < 1.30.0 >= 2.0.0, < 2.2.0

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-5h93-6whr-6q8j github.com: https://github.com/modelcontextprotocol/python-sdk/pull/3397 github.com: https://github.com/modelcontextprotocol/python-sdk/pull/3448 github.com: https://github.com/modelcontextprotocol/python-sdk/commit/2106335745563b2321b8c73fef2c12903d00aa6e github.com: https://github.com/modelcontextprotocol/python-sdk/commit/c6762e821c527925f0b617db216d00fbd1d0bf99 github.com: https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0 github.com: https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.2.0