CVE-2026-45364

high

Published 2026-05-15 · Modified 2026-05-28

💬 Discuss on Community ✚ Propose mitigation

CVSS v3

7.3

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

CVSS v4 NEW

—

not yet in upstream

VIR risk

7.3

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.

Predictions

Exploit likelihood

82%

Patch ETA

—

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

No mitigations published for this CVE yet.

The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.

✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here with source_tier=community-verified.

Package impact

Ecosystem	Package	Vulnerable	Fixed
npm	better-auth	`<1.4.17`	`1.4.17`
npm	better-auth	`>=1.5.0-beta.1,<1.5.0-beta.9`	`1.5.0-beta.9`
NPM	better-auth	`>= 1.5.0-beta.1, < 1.5.0-beta.9`	`1.5.0-beta.9`
NPM	better-auth	`< 1.4.17`	`1.4.17`

References

CWEs

CWE-307

Community-verified mitigations for this CVE will appear above when contributors publish them.

Verify integrity in audit chain (admin only). AS-IS.