Advisories for Npm/Auth-Fetch-Mcp package

auth-fetch-mcp v3.0.1 implements SSRF protection in assertSafeUrl() (src/security.ts) to block requests to private and loopback addresses. However, the isPrivateV6() function fails to detect IPv4-mapped IPv6 loopback addresses in their hex-normalized form. When an attacker supplies a URL such as http://[::ffff:127.0.0.1]:PORT/, the Node.js WHATWG URL parser silently normalizes the host to [::ffff:7f00:1]. Because net.isIPv4('7f00:1') returns false, the private-IP check is bypassed and the URL is passed to the browser or HTTP …

Cloud credential theft — server on EC2 / GCE / Azure VM. MCP client invokes auth_fetch({ url: "http://169.254.169.254/latest/meta-data/iam/security-credentials/<role>" }) and receives temporary credentials in the tool response. Or invokes download_media({ urls: […], output_dir: "/tmp/exfil" }) to persist them to disk. Internal service enumeration — MCP client probes private-range hosts (10/8, 172.16/12, 192.168/16). Each auth_fetch returns the page DOM; each download_media writes the response to disk. Loopback exploitation — server runs …