Medium severity · published Oct 27, 2026
CVE-2026-116685
Model Context Protocol Python SDK: HTTP client transports followed cross-origin redirects carrying custom headers and bodies
New
5.9
CVSS
0.4%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Confidentiality
High
Integrity
None
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 34% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
PY
python-sdk · modelcontextprotocol
>= 1.8.0, < 1.30.0; >= 2.0.0, < 2.2.0 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-116685
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-116685
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/pull/3397
github.com
https://github.com/modelcontextprotocol/python-sdk/pull/3448
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
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