CVE-2026-81091

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of data exposure.

Exploit odds

0.5% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-08-27 17:20 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-09-23 17:17 UTC Last updatedMost recent change to the record

Details

Published

2026-08-27 17:20 UTC

Last modified

2026-09-23 17:17 UTC

Exploit probability

0.5% · EPSS, next 30 days

Weakness

CWE-918 · Server-side request forgery

Record status

Deferred

Attack profile CVSS 4.0 · 8.7

Attack vector

Network

Complexity

Low

Attack requirements

None

Privileges needed

None

User interaction

None

Confidentiality

High

Integrity

None

Availability

None