ip-address: a CIDR suffix on the parsed address suppresses special-use classification and can bypass SSRF and trust-boundary checks

Summary

ip-address is a library for parsing and manipulating IPv4 and IPv6 addresses in JavaScript. From 10.1.1 until 10.2.2, every special-use classification method is built on isInSubnet, which short-circuits to false whenever the address's own subnet mask is shorter than the reference range's mask. That mask comes verbatim from the CIDR suffix on the parsed input, so appending a suffix such as /0 suppresses classification entirely: isLoopback(), isPrivate(), isLinkLocal(), isCGNAT(), isMulticast(), isUnspecified(), isBroadcast(), isULA(), and getType() all report an internal address as unremarkable, while correctForm() and address still return the real internal target. An application that builds a network trust-boundary decision on these checks, for example a filter intended to block Server-Side Request Forgery, or SSRF, may therefore treat an internal target as external and allow the request. The underlying bit comparison is correct, and mask(n) already returns the first n bits of the full parsed address independently of subnetMask; the defect is solely that the containment guard sits in the classification path. This issue is fixed in version 10.2.2.

Timeline

1. Aug 3, 2026, 7:59 PM UTCCVE published
2. Aug 4, 2026, 5:21 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: no · Technical impact: partial

3. Aug 4, 2026, 5:21 PM UTCRecord last updated

Affected versions

• beaugunderson ip-address

  From 10.1.1 · fixed in 10.2.2

• ip-addressnpm

  From 10.1.1 · fixed in 10.2.2

References 3