ssrfcheck: Server-Side Request Forgery (SSRF) and Incomplete List of Disallowed Inputs
ssrfcheck is a library that checks if a string contains a potential SSRF attack. In 1.3.0 and earlier, ssrfcheck fails to block Server-Side Request Forgery attacks when the target private IP address is encoded as an IPv4-mapped IPv6 address (e.g. http://[::ffff:127.0.0.1]/). The WHATWG URL parser built into Node.js silently normalizes the IPv4 notation inside the brackets to compressed hex form ([::ffff:7f00:1]) before the library's private-IP regex ever runs. The regex was written to match dot-notation only and therefore never matches any real input — all seven IANA private IPv4 ranges, including the AWS/GCP/Azure metadata address 169.254.16
Versions of the package ssrfcheck before 1.2.0 are vulnerable to Server-Side Request Forgery (SSRF) due to an incomplete denylist of IP address ranges. Specifically, the package fails to classify the reserved IP address space 224.0.0.0/4 (Multicast) as invalid. This oversight allows attackers to craft requests targeting these multicast addresses.