What is CVE-2026-116685?

CVE-2026-116685 is a medium-severity vulnerability in Modelcontextprotocol Python-Sdk, classified under Information Disclosure. CVSS score: 5.9/10. Published 2026-10-27.

How severe is CVE-2026-116685?

Medium severity. CVSS v3 base score is 5.9 out of 10.

Information disclosure in Modelcontextprotocol Python-Sdk

CVE-2026-116685

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.

Vulnerability class: Information Disclosure

Published 2026-10-27.

CVSS v3 metric

CVSS v3 base score 5.9 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Modelcontextprotocol Python-Sdk — versions >= 1.8.0, < 1.30.0, >= 2.0.0, < 2.2.0

Weakness classification (CWE)

CWE-200 — Information Disclosure

References

Frequently asked questions

What is CVE-2026-116685?: CVE-2026-116685 is a medium-severity vulnerability in Modelcontextprotocol Python-Sdk, classified under Information Disclosure. CVSS score: 5.9/10. Published 2026-10-27.
How severe is CVE-2026-116685?: Medium severity. CVSS v3 base score is 5.9 out of 10.