Vulnerability · Published May 28, 2026 · Assigned by GitHub_M
CVE-2026-45364Better Auth: Rate limiter keys IPv6 addresses individually and is bypassable via prefix rotation
High 7.3
In plain English
A high-severity security flaw in better-auth from better-auth. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 22% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| npm | better-auth | 1.4.17 | GHSA-p6v2-xcpg-h6xw |
| npm | better-auth | 1.5.0-beta.9 | GHSA-p6v2-xcpg-h6xw |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| better-auth | better-auth | < 1.4.17>= 1.5.0-beta.1, < 1.5.0-beta.9 |
Weakness: CWE-307 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
References
- https://github.com/better-auth/better-auth/security/advisories/GHSA-p6v2-xcpg-h6xw x_refsource_CONFIRM
- https://github.com/better-auth/better-auth/pull/7470 x_refsource_MISC
- https://github.com/better-auth/better-auth/pull/7509 x_refsource_MISC
- https://github.com/better-auth/better-auth/commit/43e719bcc0c223c7079fa0c611a9cf7ea1188254 x_refsource_MISC
- https://github.com/better-auth/better-auth/commit/57af0f7b910dcf7b1a5c0615d10b9bd56bb69bef x_refsource_MISC