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Vulnerability · Published Oct 27, 2026 · Assigned by GitHub_M

CVE-2026-116685Model Context Protocol Python SDK: HTTP client transports followed cross-origin redirects carrying custom headers and bodies

Medium 5.9

In plain English

A medium-severity information exposure in python-sdk from modelcontextprotocol. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 34% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.9Medium
Exploit odds (30 days)0.4%top 65.6% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
PyPImcp2.2.0GHSA-5h93-6whr-6q8j
PyPImcp1.30.0GHSA-5h93-6whr-6q8j

Affected products (as reported)

VendorProductVersions
modelcontextprotocol python-sdk >= 1.8.0, < 1.30.0>= 2.0.0, < 2.2.0

Weakness: CWE-200 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

References