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.
Details
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
Affected Packages
| Software | From version | Fixed in |
|---|---|---|
| better-auth | โ | โ |
| unknown | โ | โ |
References
Similar Threats
- High CVE-2026-45337
- Unknown GHSA-wxw3-q3m9-c3jr
- High CVE-2026-41427
- Critical GHSA-xg6x-h9c9-2m83
- High GHSA-x732-6j76-qmhm
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