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.
{
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/45xxx/CVE-2026-45364.json",
"cna_assigner": "GitHub_M",
"cwe_ids": [
"CWE-307"
]
}{
"source": "AFFECTED_FIELD",
"extracted_events": [
{
"introduced": "0"
},
{
"fixed": "1.4.17"
},
{
"introduced": "1.5.0-beta.1"
},
{
"fixed": "1.5.0-beta.9"
}
]
}