High [CVE-2026-54272] Server-Side Request Forgery via IPv4-mapped/NAT64 IPv6 address misclassification

ip-address is a library for parsing and manipulating IPv4 and IPv6 addresses in JavaScript. Versions 10.1.1 through 10.2.0 are vulnerable to SSRF through misclassification of IPv4-mapped/NAT64 IPv6 addresses.

Address6.getType() classifies an address by matching it against a table of known IPv6 special-use prefixes, returning Global unicast when nothing matches. That table had no entry for the IPv4-mapped range (::ffff:0:0/96), so every mapped address fell through to Global unicast; NAT64 addresses matched their own NAT64 … labels.

The boolean checks isLoopback, isUnspecified, and isMulticast compared getType() against a fixed label and so returned false, while isLinkLocal and isULA checked only the native IPv6 ranges.

The library already exposed isMapped4() and to4(), but did not apply them inside these checks, so a mapped or NAT64 address was never normalized to its embedded IPv4 address before classification. For IPv4-mapped addresses the host OS routes to the IPv4 stack, so the misclassification is reachable on any dual-stack host.

For NAT64, the classification bypass is unconditional but end-to-end reachability additionally requires a NAT64/DNS64 gateway in the deployment network. This issue has been fixed in version 10.2.1.

An attacker could exploit this misclassification to bypass network restrictions and potentially access or manipulate internal resources.