ip-address: no classifier recognizes the NAT64 local-use range 64:ff9b:1::/48, allowing SSRF and trust-boundary bypass

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

ip-address is a library for parsing and manipulating IPv4 and IPv6 addresses in JavaScript. From 10.2.0 until 10.5.1, the Address6 isPrivate classifier in src/ipv6.ts does not recognize the NAT64 local-use range 64:ff9b:1::/48. Applications that combine isPrivate, isLoopback, and isLinkLocal for a trust-boundary decision can treat an internal IPv4 destination encoded through that range as external. Exploitation depends on a server network using an operator-selected NAT64 prefix within the local-use range. A successful bypass can cross the intended network trust boundary. This issue is fixed in version 10.5.1.

Source published

28 Sep 2026 17:45:27 UTC

Source modified

28 Sep 2026 18:12:34 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 6.9 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:H/SI:N/SA:N

ip-address is a library for parsing and manipulating IPv4 and IPv6 addresses in JavaScript. From 10.2.0 until 10.5.1, the Address6 isPrivate classifier in src/ipv6.ts does not recognize the NAT64 local-use range 64:ff9b:1::/48. Applications that combine isPrivate, isLoopback, and isLinkLocal for a trust-boundary decision can treat an internal IPv4 destination encoded through that range as external. Exploitation depends on a server network using an operator-selected NAT64 prefix within the local-use range. A successful bypass can cross the intended network trust boundary. This issue is fixed in version 10.5.1.

Source published

Sep 28, 2026, 5:45:27 PM (timezone not stated)

Source modified

Sep 28, 2026, 6:12:34 PM (timezone not stated)

Observed here

11 Nov 2026 05:28:21 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 6.9 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:H/SI:N/SA:N

ip-address is a library for parsing and manipulating IPv4 and IPv6 addresses in JavaScript. From 10.2.0 until 10.5.1, the Address6 isPrivate classifier in src/ipv6.ts does not recognize the NAT64 local-use range 64:ff9b:1::/48. Applications that combine isPrivate, isLoopback, and isLinkLocal for a trust-boundary decision can treat an internal IPv4 destination encoded through that range as external. Exploitation depends on a server network using an operator-selected NAT64 prefix within the local-use range. A successful bypass can cross the intended network trust boundary. This issue is fixed in version 10.5.1.

Source published

28 Sep 2026 18:17:20 UTC

Source modified

30 Sep 2026 19:57:08 UTC

Observed here

25 Oct 2026 04:17:26 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 6.9 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:H/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

### Summary No classifier on `Address6` recognizes the NAT64 local-use range `64:ff9b:1::/48` (RFC 8215). `isPrivate()`, `isLoopback()`, `isLinkLocal()` and their siblings all return `false` for every address in it, so an internal IPv4 destination written through a local-use NAT64 prefix (`64:ff9b:1:7f00:0:100::` for `127.0.0.1`, `64:ff9b:1:a9fe:a9:fe00::` for `169.254.169.254`) reads as an ordinary global address. `getType()` names the range `'NAT64 (local-use)'`, so the library knows what the address is and classifies it as nothing. 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) will classify an internal target as external and allow the request. SSRF is an attack in which a user-supplied address coaxes the server into making a request to an internal destination the user could not otherwise reach, such as a loopback service or a cloud metadata endpoint. ### Details The fix for GHSA-22jq-vg5j-6vgg (10.2.1) classifies IPv4-mapped (`::ffff:0:0/96`) and NAT64 well-known (`64:ff9b::/96`) addresses by their embedded IPv4 address: `embeddedIPv4()` in `src/ipv6.ts` decodes the trailing 32 bits and every special-use classifier delegates to the resulting `Address4`. Those are the only two ranges `embeddedIPv4()` handles. The local-use range differs in kind from the well-known prefix, which is why extending the decoder does not fix it. RFC 8215 reserves `64:ff9b:1::/48` so an operator can carve their own NAT64 prefix out of it, of any length RFC 6052 allows (`/48`, `/56`, `/64`, or `/96`). Where the IPv4 address sits depends on that choice: `127.0.0.1` is `64:ff9b:1:7f00:0:100::` under a `/48` prefix and `64:ff9b:1::7f00:1` under a `/96` prefix, and each of those decodes to a different address under the other prefix length. There is no single embedded IPv4 address for the library to classify by. What is well-defined is the range as a whole. The IANA IPv6 Special-Purpose Address Registry lists `64:ff9b:1::/48` as not globally reachable, and Python's `ipaddress` module reports `is_private` as `True` and `is_global` as `False` for every address in it. `isPrivate()` covered ULA (`fc00::/7`) plus the decoded mapped and well-known cases, and nothing in the local-use range. ### Affected versions `>= 10.2.0, <= 10.5.0`. The `is*` classification API was extended to `Address6` in 10.2.0; releases before it do not expose the method and are not affected through this vector. ### Impact Every address in `64:ff9b:1::/48` parses successfully, `isValid()` is `true`, and no classifier catches it. Which internal target is reached depends on the NAT64 prefix deployed on the server's network; the well-known prefix column is the patched control from GHSA-22jq-vg5j-6vgg. | Internal target | Well-known form | Classified | Local-use form (`/48` prefix) | Classified | |---|---|---|---|---| | `127.0.0.1` | `64:ff9b::7f00:1` | loopback | `64:ff9b:1:7f00:0:100::` | nothing | | `10.0.0.1` | `64:ff9b::a00:1` | private | `64:ff9b:1:a00:0:100::` | nothing | | `169.254.169.254` | `64:ff9b::a9fe:a9fe` | link-local | `64:ff9b:1:a9fe:a9:fe00::` | nothing | | `192.168.1.1` | `64:ff9b::c0a8:101` | private | `64:ff9b:1:c0a8:1:100::` | nothing | ### Reachability Reaching an internal host through one of these addresses requires that the server's network run a NAT64 translator on a prefix inside `64:ff9b:1::/48` and that the attacker guess or know the prefix length. That is the same precondition the well-known prefix carries (a translator on `64:ff9b::/96`), with the additional constraint that the prefix is operator-chosen rather than fixed. The severity reflects that precondition. ### Proof of concept `npm i [email protected]`, then: ```js const { Address6 } = require('ip-address'); // A guard of the shape the library documents. function isBlocked(host) { const a = new Address6(host); return a.isLoopback() || a.isLinkLocal() || a.isPrivate() || a.isMulticast() || a.isUnspecified(); } for (const h of ['64:ff9b::7f00:1', '64:ff9b:1:7f00:0:100::', '64:ff9b:1::7f00:1']) { console.log(isBlocked(h) ? 'BLOCK' : 'ALLOW', h, '-> getType()', new Address6(h).getType()); } ``` On affected versions: ``` BLOCK 64:ff9b::7f00:1 -> getType() NAT64 (well-known) ALLOW 64:ff9b:1:7f00:0:100:: -> getType() NAT64 (local-use) ALLOW 64:ff9b:1::7f00:1 -> getType() NAT64 (local-use) ``` ### Remediation Upgrade to the patched release. In the fix, `isPrivate()` returns `true` for every address in `64:ff9b:1::/48`, alongside ULA and the decoded mapped and well-known cases. The range is reported private as a whole rather than by a decoded IPv4 address, for the reason given above; `toAddress4Nat64(prefix)` remains the way to decode an address under a known deployment prefix. `isLoopback()` and `isLinkLocal()` are unchanged for this range, since without the prefix length the library cannot know which IPv4 address is embedded. If you cannot upgrade immediately, test the range directly: ```js const NAT64_LOCAL_USE = new Address6('64:ff9b:1::/48'); const localUse = new Address6(host).isHostInSubnet(NAT64_LOCAL_USE); ``` ### A note on SSRF defense These methods are address classifiers, not a complete SSRF defense. Regardless of this fix, a robust SSRF guard must resolve the hostname and validate the *resolved* IP against the socket it connects to, and account for DNS rebinding and redirects. Treat these checks as one layer, not the only one.

Source published

28 Sep 2026 20:43:03 UTC

Source modified

28 Sep 2026 21:00:05 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:H/SI:N/SA:N

Publisher rating · MODERATE