express-rate-limit · Vulnerability

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express-rate-limit: IPv4-mapped IPv6 addresses bypass per-client rate limiting (all IPv4 clients share one bucket on dual-stack servers)

express-rate-limit is a basic rate-limiting middleware for Express. In versions starting from 8.0.0 and prior to versions 8.0.2, 8.1.1, 8.2.2, and 8.3.0, the default keyGenerator in express-rate-limit applies IPv6 subnet masking (/56 by default) to all addresses that net.isIPv6() returns true for. This includes IPv4-mapped IPv6 addresses (::ffff:x.x.x.x), which Node.js returns as request.ip on dual-stack servers. Because the first 80 bits of all IPv4-mapped addresses are zero, a /56 (or any /32 to /80) subnet mask produces the same network key (::/56) for every IPv4 client. This collapses all IPv4 traffic into a single rate-limit bucket: one client exhausting the limit causes HTTP 429 for all other IPv4 clients. This issue has been patched in versions 8.0.2, 8.1.1, 8.2.2, and 8.3.0.

Source published

7 Mar 2026 05:19:08 UTC

Source modified

9 Mar 2026 20:44:25 UTC

Saved here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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

Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

express-rate-limit is a basic rate-limiting middleware for Express. In versions starting from 8.0.0 and prior to versions 8.0.2, 8.1.1, 8.2.2, and 8.3.0, the default keyGenerator in express-rate-limit applies IPv6 subnet masking (/56 by def…

express-rate-limit is a basic rate-limiting middleware for Express. In versions starting from 8.0.0 and prior to versions 8.0.2, 8.1.1, 8.2.2, and 8.3.0, the default keyGenerator in express-rate-limit applies IPv6 subnet masking (/56 by default) to all addresses that net.isIPv6() returns true for. This includes IPv4-mapped IPv6 addresses (::ffff:x.x.x.x), which Node.js returns as request.ip on dual-stack servers. Because the first 80 bits of all IPv4-mapped addresses are zero, a /56 (or any /32 to /80) subnet mask produces the same network key (::/56) for every IPv4 client. This collapses all IPv4 traffic into a single rate-limit bucket: one client exhausting the limit causes HTTP 429 for all other IPv4 clients. This issue has been patched in versions 8.0.2, 8.1.1, 8.2.2, and 8.3.0.

Source published

Mar 7, 2026, 5:19:08 AM (timezone not stated)

Source modified

Mar 9, 2026, 8:44:25 PM (timezone not stated)

Saved here

15 Nov 2026 09:30:10 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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

Source: euvd · ENISA EUVD · source terms and attribution apply. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

EUVD CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

express-rate-limit is a basic rate-limiting middleware for Express. In versions starting from 8.0.0 and prior to versions 8.0.2, 8.1.1, 8.2.2, and 8.3.0, the default keyGenerator in express-rate-limit applies IPv6 subnet masking (/56 by def…

express-rate-limit is a basic rate-limiting middleware for Express. In versions starting from 8.0.0 and prior to versions 8.0.2, 8.1.1, 8.2.2, and 8.3.0, the default keyGenerator in express-rate-limit applies IPv6 subnet masking (/56 by default) to all addresses that net.isIPv6() returns true for. This includes IPv4-mapped IPv6 addresses (::ffff:x.x.x.x), which Node.js returns as request.ip on dual-stack servers. Because the first 80 bits of all IPv4-mapped addresses are zero, a /56 (or any /32 to /80) subnet mask produces the same network key (::/56) for every IPv4 client. This collapses all IPv4 traffic into a single rate-limit bucket: one client exhausting the limit causes HTTP 429 for all other IPv4 clients. This issue has been patched in versions 8.0.2, 8.1.1, 8.2.2, and 8.3.0.

Source published

7 Mar 2026 06:16:10 UTC

Source modified

17 Jun 2026 10:32:59 UTC

Saved here

25 Oct 2026 07:19:08 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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

Source: nvd · NIST NVD usage terms; underlying source attribution retained. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · [email protected] · Secondary · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

express-rate-limit: IPv4-mapped IPv6 addresses bypass per-client rate limiting on servers with dual-stack network

## Summary The default `keyGenerator` in express-rate-limit applies IPv6 subnet masking (`/56` by default) to all addresses that `net.isIPv6()` returns true for. This includes IPv4-mapped IPv6 addresses (`::ffff:x.x.x.x`), which Node.js returns as `request.ip` on dual-stack servers. Because the first 80 bits of all IPv4-mapped addresses are zero, a `/56` (or any `/32` to `/80`) subnet mask produces the same network key (`::/56`) for **every** IPv4 client. This collapses all IPv4 traffic into a single rate-limit bucket: one client exhausting the limit causes HTTP 429 for all other IPv4 clients. ## Details ### Root Cause In `source/ip-key-generator.ts`: ```typescript export function ipKeyGenerator(ip: string, ipv6Subnet: number | false = 56) { if (ipv6Subnet && isIPv6(ip)) { return `${new Address6(`${ip}/${ipv6Subnet}`).startAddress().correctForm()}/${ipv6Subnet}` } return ip } ``` `net.isIPv6('::ffff:192.168.1.1')` returns `true`, so IPv4-mapped addresses enter the subnet masking path. With a `/56` prefix, the start address for any `::ffff:x.x.x.x` is `::`, producing the key `::/56`. ### Proof of Concept ```javascript const { isIPv6 } = require('net'); const { Address6 } = require('ip-address'); function ipKeyGenerator(ip, ipv6Subnet = 56) { if (ipv6Subnet && isIPv6(ip)) { return `${new Address6(`${ip}/${ipv6Subnet}`).startAddress().correctForm()}/${ipv6Subnet}`; } return ip; } console.log(ipKeyGenerator('::ffff:192.168.1.1', 56)); // ::/56 console.log(ipKeyGenerator('::ffff:10.0.0.1', 56)); // ::/56 console.log(ipKeyGenerator('::ffff:8.8.8.8', 56)); // ::/56 // ALL produce '::/56' — same bucket ``` ### End-to-End Validation On a dual-stack Express server (`app.listen(port, '::')`), tested with Express 5.2.1: - `request.ip` for IPv4 clients is `::ffff:127.0.0.1` - Rate limit key resolves to `::/56` - After `limit` requests from any IPv4 client, all other IPv4 clients receive 429 ### When This Occurs - Node.js dual-stack servers (default on Linux when listening on `::`) - Any environment where `request.ip` contains IPv4-mapped IPv6 addresses - Only affects the default `keyGenerator` (custom key generators are not affected) ## Impact - **Denial of Service**: A single client can block all IPv4 traffic by exhausting the shared rate limit - **Affects default configuration**: No special options needed to trigger this ## Affected Versions All versions of express-rate-limit between v8.0.0 and v8.2.1. ## Fix This issue was fixed in commit 14e53888cdfd1b9798faf5b634c4206409e27fc4. This fix has been included in release v8.3.0, and backported to all affected minor versions in the form of releases v8.2.2, v8.1.1, and v8.0.2.

Source published

6 Mar 2026 18:36:56 UTC

Source modified

10 Sep 2026 03:50:36 UTC

Saved 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

Source: osv · GitHub Advisory Database · CC-BY-4.0. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Publisher rating · HIGH