CVE-2026-45364
Better Auth: Rate limiter keys IPv6 addresses individually and is bypassable via prefix rotation
At a glance
- Source
- NVD
- EPSS
- EPSS 0.29 % · percentile 22 ()
- State
- PUBLISHED
- Published
- Updated
- Assigner
- GitHub_M
- NVD status
- Deferred
Description
Better Auth is an authentication and authorization library for TypeScript. Prior to 1.4.17 and 1.5.0-beta.9, Better Auth's HTTP rate limiter keyed each request by the exact textual IP address it received in x-forwarded-for (or the configured IP-bearing header). IPv6 clients controlling a typical /64 allocation could rotate through 2^64 distinct source addresses without exhausting the per-address counter, defeating rate limiting on /sign-in/email, /sign-up/email, /forget-password, and every other path the limiter protects. The same bug allowed a single client to vary the textual encoding of one IPv6 address (uppercase, compression, IPv4-mapped, hex-encoded IPv4-in-IPv6) and produce multiple distinct keys. This vulnerability is fixed in 1.4.17 and 1.5.0-beta.9.
Weaknesses (CWE)
- CWE-307 — Improper Restriction of Excessive Authentication Attempts
References
- https://github.com/better-auth/better-auth/security/advisories/GHSA-p6v2-xcpg-h6xw
- https://github.com/better-auth/better-auth/pull/7470
- https://github.com/better-auth/better-auth/pull/7509
- https://github.com/better-auth/better-auth/commit/43e719bcc0c223c7079fa0c611a9cf7ea1188254
- https://github.com/better-auth/better-auth/commit/57af0f7b910dcf7b1a5c0615d10b9bd56bb69bef
Scores
| Version | Score | Vector | Scored by |
|---|---|---|---|
| CVSS 3.1 | HIGH 7.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L | GitHub_M |
| CVSS 3.1 | HIGH 7.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L | NVD · security-advisories@github.com (Secondary) |
Advisories
- GHSA-p6v2-xcpg-h6xw — Better Auth: Rate limiter keys IPv6 addresses individually and is bypassable via prefix rotation
European references
- ENISA EUVD · EUVD-2026-33073
- GCVE · GCVE-0-2026-45364
Affected products
| Product | Versions |
|---|---|
| better-auth · better-auth | affected < 1.4.17 ; affected >= 1.5.0-beta.1, < 1.5.0-beta.9 |
Sources
| Source | Licence |
|---|---|
| CVE List (CVEProject cvelistV5) | CVE Program Terms of Use |
| EPSS (FIRST.org) | FIRST — attribution requested |
| ENISA EUVD | ENISA — reproduction authorised, source acknowledged |
| NVD (NIST) via fkie-cad/nvd-json-data-feeds | Public domain — this product uses data from the NVD API but is not endorsed or certified by the NVD |