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EUVD-2026-318020

fkie_cve-2026-43929

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 169.254.169.254, are bypassed. Any application using isSSRFSafeURL() to guard HTTP requests made with user-supplied URLs is fully exposed to SSRF.

GHSA-j4rj-2jr5-m439 — ssrfcheck Vulnerable to Server-Side Request Forgery (SSRF) and Incomplete List of Disallowed Inputs

Affected: npm: ssrfcheck

### Summary

`ssrfcheck` v1.3.0 (latest) 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 `169.254.169.254`, are bypassed. Any application using `isSSRFSafeURL()` to guard HTTP requests made with user-supplied URLs is fully exposed to SSRF.

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### Details

**Vulnerable file:** `src/is-private-ip.js`

The library detects IPv6 private addresses using the `privIp6()` function. The relevant portion:

```js // src/is-private-ip.js (lines ~40-60 of the published source) function privIp6 (ip) { return /^::$/.test(ip) || /^::1$/.test(ip) || /^::f{4}:([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})$/.test(ip) || /^::f{4}:0.([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})$/.test(ip) || /^64:ff9b::([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})$/.test(ip) || // ... more patterns, all expect dot-notation ... } ```

The third line is the IPv4-mapped IPv6 check. It expects input in the form `::ffff:127.0.0.1` (dots). However, the IP is extracted from the URL using `url.ho…