Budibase: OIDC SSO account takeover: incoming identity linked by email without checking email_verified

Per OIDC Core §5.7, the email claim MUST NOT be used as an identity key unless email_verified is true. Budibase never reads the flag.

Preconditions (attack requirement — AT:P): the attacker must be able to authenticate through an IdP that the Budibase instance trusts AND get that IdP to assert the victim's email with email_verified = false. This is reachable, not exotic:

• Self-registration with an unverified email — Keycloak and Authentik ship with "Verify Email" OFF by default; if the trusted IdP allows public sign-up, the attacker registers a new account and simply enters email = <victim> at sign-up. No confirmation email is needed — the IdP stores and asserts it unverified.
• Self-service profile editing — many IdPs let a logged-in user change their own email without forced re-verification.
• Attacker-operated / federated IdP or permissive social login — where the attacker controls or influences a trusted provider, or the provider asserts a user-typed (unverified) email. It is not exploitable through a strict corporate IdP that enforces email verification (there email_verified = true and the attacker cannot claim the victim's address) — which is exactly why Budibase must check the flag rather than assume every configured IdP enforces it. The defect is unconditional on the Budibase side; the attack requirement is purely the (default, common) IdP email policy.

PoC

Reproduced live on Budibase 3.39.14 (self-hosted, community license) against a stock Keycloak 26 realm budi with default "Verify Email" = off; OIDC client registered and activated in Budibase.

Setup: a pre-existing victim global-admin Budibase account [email protected] (_id = us_1ab2dfcf…, local account, no IdP link). The attacker owns their own IdP account (attacker, distinct sub) and can set its email attribute unverified.

Step 1 — the IdP asserts the claim (proves email_verified=false):

POST /realms/budi/protocol/openid-connect/token   (Keycloak)
grant_type=password&client_id=budibase&client_secret=…&username=attacker&password=Attacker123!&scope=openid email profile
-> id_token payload: { "sub":"3cf58c45-…", "preferred_username":"attacker",
                      "email":"[email protected]", "email_verified":false }

The authenticated principal is provably attacker (its own sub/preferred_username/password), merely claiming the victim's email, unverified.

Step 2 — drive the standard OIDC flow as attacker: GET /api/global/auth/default/oidc/configs/kc-oidc-1 -> IdP login as attacker/Attacker123! -> GET /api/global/auth/oidc/callback?code=…&state=….

Step 3 — result (takeover): Budibase sets budibase:auth to a session JWT { "userId":"us_1ab2dfcf…", "email":"[email protected]", "tenantId":"default" }, and GET /api/global/self returns the victim: _id = us_1ab2dfcf…, admin.global = true, builder.global = true, providerType = oidc. The attacker authenticated as a different IdP principal with an unverified email yet now holds a full global-admin session for the victim.

Negative control (proves the email claim is the cause, not a normal self-login): A second attacker attacker2 with a benign unverified email [email protected] (matching no Budibase user) runs the identical flow:

id_token: { "sub":"55794bf2-…", "preferred_username":"attacker2", "email":"[email protected]", "email_verified":false }
-> budibase:auth: { "userId":"us_55794bf2-…" }   (a NEW account, _id derived from the IdP sub)
-> /api/global/self: { "_id":"us_55794bf2-…", "email":"[email protected]", admin.global: null, builder.global: null }

With a benign email the attacker gets their own new low-privilege account; only when the email claim equals the victim's does the same flow yield the victim's admin account. Same self-authentication, single variable changed = the unverified-email merge is the vulnerability.

Impact

Takeover of any existing Budibase account by email, including the instance owner / global admin -> full control of the tenant (apps, datasources, automations, user management, stored datasource credentials). The attacker authenticates as their own (different) IdP principal and ends up holding the victim's session and roles. The only requirement beyond a trusted IdP login is that the IdP assert the victim's email unverified — the default for a freshly-created Keycloak/Authentik realm and common in social logins (see Preconditions). Any deployment that trusts an OIDC IdP without enforced email verification is exposed; the Budibase-side flaw (ignoring email_verified) is unconditional.

Remediation

Primary fix: in the OIDC verify path, require email_verified === true before using email to look up / link an existing account; otherwise reject the login (or fall back to sub-only matching and never merge into a pre-existing local/SSO account). Concretely, thread the email_verified claim through buildJwtClaims/getEmail (oidc.ts) and gate the getGlobalUserByEmail fallback in sso.ts:57-59 on it.

Audit the whole class: apply the same email_verified (and, for SAML, EmailVerified/assertion-signature) gate to every SSO strategy that links by email — OIDC, SAML, and any social provider — not only the Google strategy (which already passes requireLocalAccount=true). Email-based account linking anywhere must require a verified email.

Defense-in-depth for operators who cannot patch immediately:

• On the IdP, enable "Verify Email" / require verified email before issuing tokens (Keycloak: realm -> Login -> Verify Email = on), and restrict which email domains the IdP will assert.
• Prefer sub-based account mapping over email in the IdP/Budibase mapping config where available.
• Audit existing accounts for unexpected OIDC links to privileged users; rotate sessions.