CVE-2026-67335

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.

Score

CVSS 4.0 6.0 Medium

Status

Deferred - disclosure@vulncheck.com

Published

2026-08-01

Last modified

2026-08-03

Weaknesses

CWE-287

Affected products

• Better-auth/oauth-provider (Better-auth)

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