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.
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Thu, 27 Aug 2026 16:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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. | |
| Title | mcp-use Inspector Proxy Server-Side Request Forgery via Caller-Supplied Target URL | |
| Weaknesses | CWE-918 | |
| References |
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| Metrics |
cvssV3_1
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MITRE
Status: PUBLISHED
Assigner: VulnCheck
Published:
Updated: 2026-08-27T14:50:32.568Z
Reserved: 2026-08-26T16:00:30.592Z
Link: CVE-2026-81091
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