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GHSA-v8vw-gw5j-w7m6
No affected components available
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
- Start the registry server locally or identify a deployed instance
- 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" /> - Observe the 308 Permanent Redirect response with Location: //evil.com:
- When accessed in a browser, the user is redirected to https://evil.com
Impact
Phishing: Attackers can abuse the trusted registry domain to redirect users to credential-harvesting pages Malware distribution: Redirect users to sites serving malicious downloads Trust abuse: Links originating from the official MCP Registry domain carry implicit trust
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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