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Fencer Vulns
high 7.5

CVE-2026-30827 json

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

published 2026-03-06 8 mo ago modified 2026-09-10 1 mo ago also GHSA-46wh-pxpv-q5gq , EUVD-2026-10113

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 44%
public exploits
0
none known

Summary

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.

Patch / fix

  • npm express-rate-limit 8.0.2, 8.1.1, 8.2.2
  • express-rate-limit_project express-rate-limit 8.0.2, 8.2.2

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-30827 updated cvss 7.5

express-rate-limit: express-rate-limit: Denial of Service for IPv4 clients due to incorrect IPv6 subnet masking

  • Red Hat Developer Hub 1 rhdh/rhdh-hub-rhel9
    affected: workaround, no fix planned “Will not fix”
  • Red Hat Self-service automation portal 2 ansible-automation-platform/automation-portal
    affected: workaround, no fix available
  • Red Hat Ansible Automation Platform 2.6 ansible-automation-platform-tech-preview 1774268173
    fixed: vendor fix RHSA-2026:6309
  • Red Hat OpenShift Dev Spaces 3.28 devspaces/openvsx-rhel9 1779528224
    fixed: vendor fix RHSA-2026:21772
  • Red Hat Ansible Automation Platform 2.6 ansible-automation-platform 1774648896, ansible-automation-platform 1774648925, ansible-automation-platform-26 1774139204, ansible-automation-platform-26 1774139334, ansible-automation-platform-26 1774153089, ansible-automation-platform-26 1774243862, +22 more Red Hat OpenShift Dev Spaces 3.28 devspaces/udi-rhel9 1779829736, devspaces/code-rhel9 1779814592, devspaces/server-rhel9 1779342423, devspaces/traefik-rhel9 1779786779, devspaces/udi-base-rhel9 1779741066, devspaces/code-sshd-rhel9 1779813519, +9 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
8 mo ago

Exploit prediction

0.52% chance of exploitation in the next 30 days, higher than 44% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/express-rate-limit/express-rate-limit/security/advisories/GHSA-46wh-pxpv-q5gq referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
npm express-rate-limit
>=8.2.0, <8.2.2
>=8.1.0, <8.1.1
>=8.0.0, <8.0.2
8.2.2
8.1.1
8.0.2

Affected products

  • express-rate-limit express-rate-limit

Classification

Weakness
  • CWE-770 Allocation of Resources Without Limits or Throttling

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.