Bug 2445429 (CVE-2026-30827)

Summary: CVE-2026-30827 express-rate-limit: express-rate-limit: Denial of Service for IPv4 clients due to incorrect IPv6 subnet masking
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: abarbaro, alizardo, dschmidt, erezende, jchui, jhe, jlanda, jwong, kshier, ktsao, nboldt, omaciel, psrna, sdawley, simaishi, smcdonal, stcannon, teagle, yguenane
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
A flaw was found in express-rate-limit. The default key generator incorrectly applies IPv6 subnet masking to IPv4-mapped IPv6 addresses, which are used when an IPv4 client connects to a dual-stack server. This misconfiguration causes all IPv4 traffic to be treated as a single entity for rate limiting. Consequently, a remote attacker can exhaust the rate limit with a single client, leading to a Denial of Service (DoS) for all other IPv4 clients by causing them to receive HTTP 429 errors.
 Story Points: ---
Clone Of: Environment:
Last Closed: Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-03-07 06:01:29 UTC 
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.