Information disclosure in MCP Python SDK - CVE-2026-116685
Published: November 9, 2026
Vulnerability identifier: #VU163095
CSH Severity: Medium
CVSS v4: 8.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-116685
CWE-ID: CWE-200
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows an unauthenticated remote attacker to capture credentials in custom headers and sensitive request bodies sent by MCP Python SDK clients.
The vulnerability exists due to unrestricted cross-origin redirect following in the HTTP transports and OAuth providers when a trusted endpoint redirects requests to another origin. An unauthenticated remote attacker can influence that endpoint's redirects to receive custom headers and, with HTTP 307 or 308 redirects, replayed request bodies.
Affected software
MCP Python SDK
How to mitigate CVE-2026-116685
Install security update from vendor's website.
MCP Python SDK - addressed in versions 1.30.0, 2.2.0