CVE-2026-67335: better-auth before 1.6.2 OAuth State Validation Bypass

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-01 · updated 2026-09-08
Weakness: CWE-287

Description

better-auth versions before 1.6.2 fail to validate the OAuth state parameter against the stored nonce when using cookie-backed state storage without PKCE. Attackers can forge the state parameter and supply an attacker-controlled authorization code to create authenticated sessions bound to the attacker's external identity or persistently link attacker accounts to victim profiles.

Affected products

better-auth: before 1.6.2 — fixed in 1.6.2

How to fix

Upgrade to a fixed version: better-auth 1.6.2. Check the vendor advisory for mitigations.

References

https://github.com/better-auth/better-auth/security/advisories/GHSA-wxw3-q3m9-c3jr
https://www.vulncheck.com/advisories/better-auth-before-oauth-state-validation-bypass

Get alerted when CVE-2026-67335 or the next vulnerability affects your stack