CVE-2026-30827 Details
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.
A denial-of-service vulnerability has been identified in the express-rate-limit middleware for Express, affecting versions 8.0.0 prior to 8.0.2, as well as 8.1.1, 8.2.2, and 8.3.0. The issue arises because the default keyGenerator applies IPv6 subnet masking to all addresses recognized as IPv6 by Node.js. This includes IPv4-mapped IPv6 addresses, which are treated as regular IPv6 addresses on dual-stack servers. The subnet masking collapses all IPv4 traffic into a single rate-limit bucket, allowing one client to exhaust the limit for all IPv4 clients, causing them to receive HTTP 429 responses.
Users can upgrade to express-rate-limit versions 8.3.0, 8.2.2, 8.1.1, or 8.0.2 to address this vulnerability.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Mar 9, 2026References to Advisories, Solutions, and Tools
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Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-770 | Allocation of Resources Without Limits or Throttling | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| express-rate-limit project express-rate-limit | >= 8.0.0, < 8.0.2 >= 8.2.0, < 8.2.2 8.1.0 |
CPE
Remediation
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Change History
4 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| Mar 11, 2026 | Initial Analysis | [email protected] |
| Mar 7, 2026 | New CVE Received | [email protected] |