CVE-2026-44427: Model Context Protocol Registry open redirect in TrailingSlashMiddleware

Executive brief

The MCP Registry, a component used for managing Model Context Protocol resources, is vulnerable to an open redirect flaw. Attackers can create malicious links that appear to belong to the trusted registry domain but instead redirect users to external, potentially harmful websites. This can be used in phishing campaigns to steal credentials or distribute malware by exploiting the user's trust in the official domain.

Technical details

The TrailingSlashMiddleware in internal/api/server.go is vulnerable to an open redirect (CWE-601). The middleware strips trailing slashes from request paths and issues a 308 Permanent Redirect to the cleaned path without proper validation. An attacker can craft a URL using a protocol-relative path (e.g., //evil.com/) which, when processed, results in a Location header that browsers interpret as an absolute external URL. This allows remote attackers to redirect users to arbitrary domains. The issue is fixed in version 1.7.5.

Affected products

• modelcontextprotocol registry >= 1.1.0, < 1.7.5

Timeline

• 2026-05-04: disclosed
• 2026-05-08: advisory: GitHub Advisory published
• 2026-05-14: other: NVD published

References

• https://api.github.com/users/gujasec
• https://github.com/gujasec
• https://api.github.com/users/gujasec/gists%7B/gist_id%7D
• https://api.github.com/users/gujasec/repos
• https://avatars.githubusercontent.com/u/43931578?v=4
• https://api.github.com/users/gujasec/events%7B/privacy%7D