MCP Registry has open redirect via protocol-relative path in trailing-slash middleware

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

5.7 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P · score source

EPSS

• CVE-2026-44427: 0.47% estimated exploitation activity in the next 30 days; percentile 40.68 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The TrailingSlashMiddleware in internal/api/server.go is vulnerable to an open redirect attack. An attacker can craft a URL with a protocol-relative path (e.g., //evil.com/) that, after trailing slash removal, results in a Location header of //evil.com — which browsers interpret as an absolute URL to an external domain. Details The TrailingSlashMiddleware strips trailing slashes from request paths and issues a 308 Permanent Redirect to the cleaned path. However, it does not validate or sanitize the resulting path before using it as the redirect target. When a request is made with a path like //evil.com/, the middleware processes it as follows: PoC 1. Start the registry server locally or identify a deployed instance 2. Send a request with a double-slash path followed by an external domain: curl -v https://<registry-host//evil.com/ <img width="3066" height="969" alt="image" src="https://github.com/user-attachments/assets/a5305f00-29bf-4708-952a-478d608f2074" / 3. Observe the…

Published by the source

8 May 2026, 17:02 UTC

Last modified by the source

15 May 2026, 23:47 UTC

Source last checked

26 Oct 2026, 15:22 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-v8vw-gw5j-w7m6

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# Patch Next advisory brief: CVE-2026-44427

Advisory: MCP Registry has open redirect via protocol-relative path in trailing-slash middleware
IDs: CVE-2026-44427, GHSA-v8vw-gw5j-w7m6
Record: https://patchnext.com/advisories/cve-2026-44427 (revision 1, source checked 26 Oct 2026, 15:22 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/modelcontextprotocol/registry 1.7.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/modelcontextprotocol/registry: affected >= 1.1.0, < 1.7.5; fixed in 1.7.5

## Suggested inspection (read-only)
- Go github.com/modelcontextprotocol/registry: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/modelcontextprotocol/registry.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-v8vw-gw5j-w7m6 (GitHub-reviewed advisory GHSA-v8vw-gw5j-w7m6 lists affected ranges: Go github.com/modelcontextprotocol/registry >=1.1.0 <1.7.5)

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