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.

Database specific

{
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
        "CWE-770"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/30xxx/CVE-2026-30827.json"
}

References

Affected packages

Git / github.com/express-rate-limit/express-rate-limit

Affected ranges

Type

GIT

Repo

https://github.com/express-rate-limit/express-rate-limit

Events

Introduced

c299d5c89f9a75e52bfc28b81c22df0f059520e8

Fixed

54a685fbc4e8f88839349677e54e52380ad374c8

Database specific

{
    "versions": [
        {
            "introduced": "8.0.0"
        },
        {
            "fixed": "8.0.2"
        }
    ]
}

Type

GIT

Repo

https://github.com/express-rate-limit/express-rate-limit

Events

Introduced

60619359e1a479cceaf5893c0eb4ec68a99d5347

Fixed

1c572187e1e70672ec75761d561be8df3d304931

Database specific

{
    "versions": [
        {
            "introduced": "8.1.0"
        },
        {
            "fixed": "8.1.1"
        }
    ]
}

Type

GIT

Repo

https://github.com/express-rate-limit/express-rate-limit

Events

Introduced

37347330ecb5e0f6e34a278fa77502b3572f57f7

Fixed

a009ad6488448515b219eb9f4203c725eb328c8e

Database specific

{
    "versions": [
        {
            "introduced": "8.2.0"
        },
        {
            "fixed": "8.2.2"
        }
    ]
}

Affected versions

v8.*

v8.0.0

v8.0.1

v8.1.0

v8.2.0

v8.2.1

Database specific

source

"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-30827.json"