Vulnerability · Published Mar 7, 2026 · Assigned by GitHub_M
CVE-2026-30827express-rate-limit: IPv4-mapped IPv6 addresses bypass per-client rate limiting (all IPv4 clients share one bucket on dual-stack servers)
High 7.5
In plain English
A high-severity resource allocation without limits in express-rate-limit from express-rate-limit. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 44% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| npm | express-rate-limit | 8.2.2 | GHSA-46wh-pxpv-q5gq |
| npm | express-rate-limit | 8.1.1 | GHSA-46wh-pxpv-q5gq |
| npm | express-rate-limit | 8.0.2 | GHSA-46wh-pxpv-q5gq |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| express-rate-limit | express-rate-limit | >= 8.0.0, < 8.0.2>= 8.1.0, < 8.1.1>= 8.2.0, < 8.2.2 |
Weakness: CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H