CVE-2026-45364

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.

CVSS v3.1 Score

7.3

HIGH

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

EPSS — Exploit Prediction

0.0030

Probability of exploitation

0.21%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-307 CWE-307

References

Other References

https://github.com/better-auth/better-auth/commit/43e719bcc0c223c7079fa0c611a9cf7ea1188254 https://github.com/better-auth/better-auth/commit/57af0f7b910dcf7b1a5c0615d10b9bd56bb69bef https://github.com/better-auth/better-auth/pull/7470 https://github.com/better-auth/better-auth/pull/7509 https://github.com/better-auth/better-auth/security/advisories/GHSA-p6v2-xcpg-h6xw

Frequently Asked Questions

What is CVE-2026-45364? +

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. It has a CVSS v3.1 base score of 7.3 (HIGH).

How severe is CVE-2026-45364? +

CVE-2026-45364 has a CVSS v3.1 score of 7.3 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0030, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-45364? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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