High 7.3Published May 28, 2026

CVE-2026-45364Better Auth: Rate limiter keys IPv6 addresses individually and is bypassable via prefix rotation

Updated under an hour ago (Oct 27, 2026, 12:20 PM ET)

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No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

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.

CVSS: 7.3 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
Weakness (CWE): CWE-307
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Deferred
Record last updated: May 29, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

better-auth better-auth better_auth:better_auth (from the name)	before 1.4.17; from 1.5.0-beta.1, < 1.5.0-beta.9	CNA record

References

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

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.