CVE-2026-67333: better-auth before 1.6.13 Stored XSS via javascript redirect_uri

Severity: high (CVSS 7.2 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-79

Description

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.

Affected products

better-auth: before 1.6.13; from 1.7.0-beta.0 before 1.7.0-beta.4 — fixed in 1.6.13, 1.7.0-beta.4

How to fix

Upgrade to a fixed version: better-auth 1.6.13, 1.7.0-beta.4. Check the vendor advisory for mitigations.

References

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