CVE-2026-45364
Better Auth: Rate limiter keys IPv6 addresses individually and is bypassable via prefix rotation
- Published
- Updated
- Reserved
- Assigned by
- GitHub_M
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.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 3.1 | High7.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L |
| NVDNVD · Deferred | 3.1 | High7.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L |
- EPSS (exploitation in 30 days)
- 0.29% · top 78% of all CVEs (7 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: yes · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.3.
Weakness
Affected products
- affected < 1.4.17
- affected >= 1.5.0-beta.1, < 1.5.0-beta.9
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- npmbetter-authGHSA-p6v2-xcpg-h6xw (opens in a new tab)
References (5)
- https://github.com/better-auth/better-auth/security/advisories/GHSA-p6v2-xcpg-h6xw (opens in a new tab)x_refsource_CONFIRM
- https://github.com/better-auth/better-auth/pull/7470 (opens in a new tab)x_refsource_MISC
- https://github.com/better-auth/better-auth/pull/7509 (opens in a new tab)x_refsource_MISC
- https://github.com/better-auth/better-auth/commit/43e719bcc0c223c7079fa0c611a9cf7ea1188254 (opens in a new tab)x_refsource_MISC
- https://github.com/better-auth/better-auth/commit/57af0f7b910dcf7b1a5c0615d10b9bd56bb69bef (opens in a new tab)x_refsource_MISC
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-p6v2-xcpg-h6xw (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2026-45364)Record last updated .