CVE-2026-81091
HighCVSS 8.6Exploitation Probability (EPSS)
Low risk27th percentile - higher than 27% of all known CVEs
Summary
The proxy middleware in mcp-use's inspector forwards requests to a destination named by the caller without inspecting the host. Loopback, link-local and private addresses were accepted, and validation was not reapplied to redirects. A caller could make the server issue requests to addresses reachable only from the host and read the responses. The current code calls isSafeProxyTarget, which checks addresses before proxying and bounds redirects.
Risk Assessment
Ability to send requests to internal addresses may lead to disclosure of sensitive information or attacks on internal services.
Recommendation
Upgrade mcp-use to a patched version that implements isSafeProxyTarget.
Original NVD description (English source)
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.