CVE-2026-49857

Name of the Vulnerable Software and Affected Versions auth-fetch-mcp versions prior to 3.0.1

Description A Server-Side Request Forgery (SSRF) issue exists due to improper validation of IPv4-mapped IPv6 addresses. The isPrivateV6() function in src/security.ts, which is called by assertSafeUrl(), fails to detect loopback addresses when they are provided in a hex-normalized form. When a URL like http://[::ffff:127.0.0.1]:PORT/ is used, the Node.js WHATWG URL parser normalizes the host to [::ffff:7f00:1]. Since net.isIPv4('7f00:1') returns false, the security check is bypassed, allowing the tool to make requests to internal loopback services.

This affects the auth fetch and download media tools, which use the url and urls[] parameters respectively. An attacker could potentially read responses from local development servers, admin panels, or metadata services.

Recommendations Update to version 3.0.1. As a temporary workaround, restrict the use of the url parameter in the auth fetch tool and the urls[] parameter in the download media tool to trusted domains only.