express-rate-limit up to 8.0.1/8.1.0/8.2.1 IPv6 Address net.isIPv6 allocation of resources

Summaryinfo

A vulnerability was found in express-rate-limit up to 8.0.1/8.1.0/8.2.1. It has been declared as problematic. This impacts the function net.isIPv6 of the component IPv6 Address Handler. Executing a manipulation can lead to allocation of resources. This vulnerability is registered as CVE-2026-30827. It is possible to launch the attack remotely. No exploit is available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability has been found in express-rate-limit up to 8.0.1/8.1.0/8.2.1 and classified as problematic. This vulnerability affects the function net.isIPv6 of the component IPv6 Address Handler. The manipulation with an unknown input leads to a allocation of resources vulnerability. The CWE definition for the vulnerability is CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. As an impact it is known to affect availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-30827 since 03/05/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1499.

Upgrading to version 8.0.2, 8.1.1 or 8.2.2 eliminates this vulnerability. Applying the patch 14e53888cdfd1b9798faf5b634c4206409e27fc4 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2026-0935). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Affected

• Amazon Linux 2
• Red Hat Enterprise Linux
• SUSE Linux
• Red Hat Ansible Automation Platform

Productinfo

Name

• express-rate-limit

Version

• 8.0
• 8.0.0
• 8.0.1
• 8.1.0
• 8.2.0
• 8.2.1

License

• open-source

Website

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

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VulDB is the best source for vulnerability data and more expert information about this specific topic.

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