# 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.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 27 Aug 2026
- **Updated:** 29 Aug 2026
- **Also known as:** GHSA-23qx-5wch-w72w, GHSA-f2jg-rm2x-hc5p

## 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 (Server-Side Request Forgery)

## 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.

## Is CVE-2026-81091 being exploited?

There is no known exploitation of CVE-2026-81091 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-81091 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-81091 in the wild and no public exploit code.

Affected product: mcp-use. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-81091/ (Markdown: https://insights.sbomify.com/CVE-2026-81091/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-81091
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-81091
- OSV: https://osv.dev/vulnerability/CVE-2026-81091

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-81091/
Summaries are generated and may contain mistakes; the official description above is the record.