ip-address: isInSubnet() and isHostInSubnet() compare addresses of different families as if they shared an address space, allowing an allowlist check to admit an address outside its range

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.3 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-101912: 0.37% estimated exploitation activity in the next 30 days; percentile 31.04 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary isInSubnet() and isHostInSubnet() accept an address of either family and compare masked binary strings without checking that both operands are the same family. Address4 pads to 32 bits and Address6 to 128, so whenever the leading bits agree the strings are equal: new Address6('a00::1').isInSubnet(new Address4('10.0.0.0/8')) is true, and new Address4('32.0.0.1').isInSubnet(new Address6('2000::/3')) is true. No IPv4 address is inside an IPv6 network, so both answers are untrue. An application that parses untrusted input as whichever family accepts it and then tests the result against a fixed-family allowlist can admit an address outside the list. Details Both methods are in src/common.ts: mask(n) returns the first n bits of the address as a string of 0 and 1, taken from a representation padded to the family's width. new Address6('a00::1').mask(8) is '00001010', and so is new Address4('10.0.0.0/8').mask(), so string equality reports containment. The signature admits either…

Published by the source

29 Sep 2026, 23:46 UTC

Last modified by the source

30 Sep 2026, 00:00 UTC

Source last checked

26 Oct 2026, 13:06 UTC

1. Revision 4 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-j6r3-76f7-8jcv

2. Revision 3 · amended · 24 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-j6r3-76f7-8jcv

4. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-j6r3-76f7-8jcv

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# Patch Next advisory brief: CVE-2026-101912

Advisory: ip-address: isInSubnet() and isHostInSubnet() compare addresses of different families as if they shared an address space, allowing an allowlist check to admit an address outside its range
IDs: CVE-2026-101912, GHSA-j6r3-76f7-8jcv
Record: https://patchnext.com/advisories/cve-2026-101912 (revision 4, source checked 26 Oct 2026, 13:06 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: ip-address 10.7.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm ip-address: affected <= 10.7.0; fixed in 10.7.1

## Suggested inspection (read-only)
- `npm ls ip-address --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on ip-address.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-j6r3-76f7-8jcv (GitHub-reviewed advisory GHSA-j6r3-76f7-8jcv lists affected ranges: npm ip-address >=0 <=10.7.0)
- Verified: https://osv.dev/vulnerability/GHSA-j6r3-76f7-8jcv (OSV record GHSA-j6r3-76f7-8jcv lists affected ranges: npm ip-address >=0 <10.7.1 (fixed))

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