Executive brief
Budibase is a low-code application platform that uses OIDC/OAuth for single sign-on authentication. The system links incoming SSO identities to existing Budibase accounts based solely on email address, without verifying that the email has been confirmed by the identity provider. An attacker can exploit this by registering at a configured IdP (such as Keycloak) with an unverified email matching an existing Budibase user, then logging in to take over that user's account, including administrative privileges.
Technical details
The vulnerability is an authentication bypass in Budibase's OIDC login flow. The SSO handler attempts to match incoming IdP identities by the OIDC subject claim (sub); when that fails (e.g., a fresh attacker account), it silently falls back to matching by email address alone, without consulting the email_verified claim from the ID token. Per OIDC Core §5.7, the email claim must not be used for account linking unless email_verified is true. The vulnerable code paths are in packages/backend-core/src/middleware/passport/sso/oidc.ts (getEmail function at lines 113–135, which never reads email_verified) and sso.ts (fallback matching at lines 57–59). An attacker with access to a trusted IdP that permits self-registration or email editing (common defaults in Keycloak and Authentik) can register or modify an account to claim the victim's email with email_verified=false, then authenticate via Budibase's OIDC flow to inherit the victim's account ID, roles, and permissions. The attack has been reproduced against Budibase 3.39.14 with stock Keycloak. The fix is available in version 3.40.0 and later.
Affected products
- Budibase Budibase < 3.40.0
Timeline
- 2026-07-24: disclosed
- 2026-07-24: patched: Version 3.40.0 released with fix