Resource exhaustion in Express-Rate-Limit
CVE-2026-30827
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
EPSS: 0.005 (43.2th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 43rd percentile — 43.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: +0.001
Affected products
- Express-Rate-Limit — versions >= 8.0.0, < 8.0.2, >= 8.1.0, < 8.1.1, >= 8.2.0, < 8.2.2
- Express-Rate-Limit Project — versions 8.1.0
Weakness classification (CWE)
References
- github.com/express-rate-limit/express-rate-limit/security/advisories/GHSA-46wh-… (Exploit, Patch, Vendor Advisory)
- github.com/express-rate-limit/express-rate-limit/commit/14e53888cdfd1b9798faf5b… (Patch)
Frequently asked questions
- What is CVE-2026-30827?
- CVE-2026-30827 is a high-severity vulnerability in Express-Rate-Limit, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 7.5/10. Published 2026-03-07.
- How severe is CVE-2026-30827?
- High severity. CVSS v3 base score is 7.5 out of 10.