XSS in Better-Auth
CVE-2026-67333
better-auth before 1.6.13 (and pre-release builds 1.7.0-beta.0 through 1.7.0-beta.3) fail to validate the scheme of redirect_uris registered via the deprecated oidc-provider plugin and the mcp plugin (which wraps the same provider). An attacker can register an OAuth client with a javascript: redirect_uri, which the authorization server later returns unchanged in the consent response. If the deployment's consent page navigates the browser to the returned redirectURI (e.g. assigning it to window.location.href), the attacker's JavaScript executes in the authorization-server origin, exposing the victim's session and enabling account takeover.
Vulnerability class: XSS (Cross-Site Scripting)
EPSS: 0.002 (5.3th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 7.2 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N.
Affected products
- Better-auth — versions 0, 1.6.13, 1.7.0-beta.0
Weakness classification (CWE)
References
- disclosure@vulncheck.com (vendor-advisory)
- disclosure@vulncheck.com (third-party-advisory)
Frequently asked questions
- What is CVE-2026-67333?
- CVE-2026-67333 is a high-severity vulnerability in Better-Auth, classified under Cross-site Scripting. CVSS score: 7.2/10. Published 2026-08-01.
- How severe is CVE-2026-67333?
- High severity. CVSS v3 base score is 7.2 out of 10.