What’s Vulnerable › Vulnerabilities

CVE-2026-15144: @fastify/rate-limit vulnerable to rate-limit bypass via IPv6 address rotation

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-29 · updated 2026-08-05
• Weakness: CWE-307

Description

@fastify/rate-limit before 11.2.0 keys rate-limit buckets by the verbatim client IP string returned from request.ip. Because a single IPv6 client can control a large address range (a /64 holds 2^64 distinct addresses) and the same address has multiple valid textual representations, an IPv6 capable client can defeat the rate-limit boundary by rotating addresses or by rewriting the same address in different forms. Applications that use @fastify/rate-limit to protect endpoints such as authentication, password reset, OTP delivery, or expensive API calls can be bypassed by IPv6 clients behind a proxy that surfaces IPv6 to the origin when trustProxy is enabled. The issue is fixed in @fastify/rate-limit 11.2.0, where the default key generator normalizes IPv6 addresses to their canonical form, collapses IPv4 mapped IPv6 to IPv4, and applies a configurable prefix mask (default /64) via a new ipv6Subnet option.

Affected products

• @fastify/rate-limit: before 11.2.0 — fixed in 11.2.0

How to fix

Upgrade to a fixed version: @fastify/rate-limit 11.2.0. Check the vendor advisory for mitigations.

References

• https://cna.openjsf.org/security-advisories.html
• https://github.com/fastify/fastify-rate-limit/security/advisories/GHSA-grpc-p53c-r64v

Get alerted when CVE-2026-15144 or the next vulnerability affects your stack