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.
History

Fri, 29 May 2026 19:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Fri, 29 May 2026 01:15:00 +0000

Type Values Removed Values Added
First Time appeared Better-auth
Better-auth better Auth
Vendors & Products Better-auth
Better-auth better Auth

Thu, 28 May 2026 22:15:00 +0000

Type Values Removed Values Added
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.
Title Better Auth: Rate limiter keys IPv6 addresses individually and is bypassable via prefix rotation
Weaknesses CWE-307
References
Metrics cvssV3_1

{'score': 7.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-05-29T19:05:38.845Z

Reserved: 2026-05-12T00:51:29.085Z

Link: CVE-2026-45364

cve-icon Vulnrichment

Updated: 2026-05-29T19:05:31.273Z

cve-icon NVD

Status : Received

Published: 2026-05-28T22:17:00.633

Modified: 2026-05-28T22:17:00.633

Link: CVE-2026-45364

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-05-29T01:00:12Z