CVE-2026-116685 · GHSA-5h93-6whr-6q8j
Model Context Protocol Python SDK: HTTP client transports followed cross-origin redirects carrying custom headers and bodies
- Risk score
- 45/100
- CVSS
- 5.9 v3.1
- Published
- 27 Oct 2026
Open in the live forecast Today's forecast
What to know
- What it is
- 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 …
- Affected
- mcp (pip) >= 2.0.0, < 2.2.0; mcp (pip) >= 1.8.0, < 1.30.0
- Fix
- Upgrade mcp to 2.2.0 or 1.30.0 (whichever matches your release line) or later.
- Exploitation
- No known exploitation
Story map
At a glance
mcp: Yellow, plan it in. The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). From 1.8.0 until 1.30.0 and 2.2.0, stateful Streamable HTTP servers, including FastMCP, MCPServer, Server.streamable_http_app(), and StreamableHTTPSessionManager, retain session entries without an idle expiration or…
The flaws
- CVE-2026-116685: Model Context Protocol Python SDK: HTTP client transports followed cross-origin redirects carrying custom headers and bodies (CVSS 5.9)
- CVE-2026-59951: MCP Python SDK: Unbounded Session Accumulation in StreamableHTTP Transport Enables Resource Exhaustion (CVSS 6.9 · EPSS 0%)
- CVE-2026-116684: Model Context Protocol Python SDK: Server bearer-token authentication accepts tokens issued for a different resource server (CVSS 6.8)
- CVE-2026-116686: Model Context Protocol Python SDK: Client fetched server-chosen $ref URLs while validating tool results against output schemas (CVSS 6.5)
The fix
Upgrade mcp: 1.30.0 · 2.2.0 or later on your release line
Who is exposed: mcp (pip) >= 1.8.0, < 1.30.0; mcp (pip) >= 2.0.0, < 2.2.0
Where it stands
- No known exploitation
Connects to
- Same weakness: Information disclosure (CWE-200). 247 other warnings in 30 days
Why it is Yellow
- CVSS 5.9 medium
- On your watchlist: python, PyPI
Affected packages
| Package | Ecosystem | Vulnerable | Fixed in |
|---|---|---|---|
| mcp | pip | >= 2.0.0, < 2.2.0 | 2.2.0 |
| mcp | pip | >= 1.8.0, < 1.30.0 | 1.30.0 |
References
- https://github.com/modelcontextprotocol/python-sdk/commit/2106335745563b2321b8c73fef2c12903d00aa6e
- https://github.com/modelcontextprotocol/python-sdk/commit/c6762e821c527925f0b617db216d00fbd1d0bf99
- https://github.com/modelcontextprotocol/python-sdk/pull/3397
- https://github.com/modelcontextprotocol/python-sdk/pull/3448
- https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0
- https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.2.0
- https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-5h93-6whr-6q8j
- https://github.com/advisories/GHSA-5h93-6whr-6q8j
- https://github.com/advisories/GHSA-5h93-6whr-6q8j
Original 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.
Last activity 27 Oct 2026. Patch Forecast updates every hour.