CVE-2026-81091 mcp-use Inspector Proxy Server-Side Request Forgery via Caller-Supplied Target URL
Attackers can force the MCP inspector proxy to send requests to internal network addresses and read responses, bypassing network restrictions.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-81091?
CVE-2026-81091 is a high-severity server-side request forgery vulnerability in mcp-use, published on 27 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
The proxy middleware in mcp-use's inspector forwards requests to a destination the caller names. mountMcpProxy in libraries/typescript/packages/inspector/src/server/proxy/mcp-proxy.ts read the target from the X-Target-URL header or the __mcp_target parameter and proxied to it without inspecting the host, so loopback, link-local and private addresses were all accepted, as were names that resolve to them, and the validation was not reapplied to a redirect the destination returned. A caller could therefore make the server issue requests to addresses reachable only from the host it runs on and read the responses. The current code calls isSafeProxyTarget, which checks the resolved address against private, loopback and link-local ranges before proxying and bounds the number of redirects followed.
Weakness: CWE-918
Which versions are affected by CVE-2026-81091?
How do I fix CVE-2026-81091?
No fix has been published for CVE-2026-81091 yet. Limit exposure of the affected software until one is available.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-81091 being exploited?
There is no known exploitation of CVE-2026-81091 in the wild and no public exploit code.
Sources
Also known as GHSA-23qx-5wch-w72w, GHSA-f2jg-rm2x-hc5p.