better-auth Better Auth up to 1.4.16/1.5.0-beta.8 Header X-Forwarded-For excessive authentication

Summaryinfo

A vulnerability was found in better-auth Better Auth up to 1.4.16/1.5.0-beta.8. It has been classified as problematic. Affected is an unknown function of the component Header Handler. Performing a manipulation of the argument X-Forwarded-For results in excessive authentication. This vulnerability was named CVE-2026-45364. The attack may be initiated remotely. There is no available exploit. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability, which was classified as problematic, was found in better-auth Better Auth up to 1.4.16/1.5.0-beta.8. This affects an unknown code block of the component Header Handler. The manipulation of the argument X-Forwarded-For with an unknown input leads to a excessive authentication vulnerability. CWE is classifying the issue as CWE-307. The product does not implement sufficient measures to prevent multiple failed authentication attempts within a short time frame, making it more susceptible to brute force attacks. This is going to have an impact on confidentiality. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-45364 since 05/12/2026. The exploitability is told to be difficult. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1110.001 for this issue.

Upgrading to version 1.4.17 or 1.5.0-beta.9 eliminates this vulnerability. Applying the patch 43e719bcc0c223c7079fa0c611a9cf7ea1188254 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Vendor

• better-auth

Name

• Better Auth

Version

• 1.4.0
• 1.4.1
• 1.4.2
• 1.4.3
• 1.4.4
• 1.4.5
• 1.4.6
• 1.4.7
• 1.4.8
• 1.4.9
• 1.4.10
• 1.4.11
• 1.4.12
• 1.4.13
• 1.4.14
• 1.4.15
• 1.4.16
• 1.5.0-beta.0
• 1.5.0-beta.1
• 1.5.0-beta.2
• 1.5.0-beta.3
• 1.5.0-beta.4
• 1.5.0-beta.5
• 1.5.0-beta.6
• 1.5.0-beta.7
• 1.5.0-beta.8

License

• open-source

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CPE 2.2info

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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