CVE-2026-43929 ssrfcheck: Server-Side Request Forgery (SSRF) and Incomplete List of Disallowed Inputs
Attackers can bypass SSRF protections in ssrfcheck using IPv4-mapped IPv6 addresses to access internal resources or cloud metadata.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-43929?
CVE-2026-43929 is a high-severity server-side request forgery vulnerability in felippe-regazio ssrfcheck, published on 12 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2026-43929?
2 open source packages ship an affected version, including ssrfcheck.
| Package | Affected | Fixed in |
|---|---|---|
ssrfcheck npm | All versions to 1.3.0 | None |
ssrfcheck npm | All versions to 1.3.0 | None |
How do I fix CVE-2026-43929?
No fix has been published for CVE-2026-43929 yet. Limit exposure of the affected software until one is available.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-43929 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-43929 exists.
Sources
Also known as GHSA-j4rj-2jr5-m439.