# External-authentication account takeover: external login linked to a pre-existing account by email without requiring verification
**Package:** @vendure/core (vendure-ecommerce/vendure, latest master) ·
> [!IMPORTANT]
> This vulnerability **only affects deployments that use external / social authentication**
(an `AuthenticationStrategy` other than the built-in native email/password strategy) where
that strategy can return an email address the external provider has **not verified** the
user owns.
**You are affected if all of these are true:**
- Your store configures one or more external `AuthenticationStrategy` implementations
(custom OAuth / social login / SSO), **and**
- At least one forwards an `emailAddress` to `ExternalAuthenticationService` without
guaranteeing the provider verified ownership of it (e.g. it doesn't check the provider's
`email_verified` claim, or leaves `verified` unset/false), **and**
- Customer accounts exist that share an email address with those external identities.
**You are NOT affected if:**
- You use only the built-in native (email/password) authentication with no external strategies, **or**
- Every external strategy you use only ever returns provider-verified emails (and sets `verified: true`).
**Remediation:** Upgrade to **3.7.0**. After upgrading, an external login is only linked to a
pre-existing account when the email is verified; a custom `AuthenticationStrategy` must set
`verified: true` only for emails the provider has actually verified.
## Summary
`ExternalAuthenticationService.createCustomerAndUser()` links a newly-presented external (OAuth/social) authentication method to a **pre-existing User account selected purely by email-address match**, and it does so **without requiring `config.verified === true`**. If any configured `AuthenticationStrategy` forwards an email that was not proven to belong to the external identity (the classic `email_verified` omission — common with custom OAuth providers, or providers/strategies that don't validate email ownership), an attacker can register at that provider using a victim's email address, authenticate, and have their external identity bound to the victim's existing Vendure account — resulting in account takeover.
## Vulnerable code
`packages/core/src/service/helpers/external-authentication/external-authentication.service.ts` — `createCustomerAndUser`:
```ts
const existingUser = await this.findExistingCustomerUserByEmailAddress(ctx, config.emailAddress);
if (existingUser) {
user = existingUser; // <-- links to the EXISTING account, by email alone
} else {
user = new User({ identifier: config.emailAddress, verified: config.verified || false, ... });
}
const authMethod = await this.connection.getRepository(ctx, ExternalAuthenticationMethod).save(
new ExternalAuthenticationMethod({ externalIdentifier: config.externalIdentifier, strategy: config.strategy }),
);
user.authenticationMethods = [...(user.authenticationMethods || []), authMethod]; // <-- external login attached
await this.connection.getRepository(ctx, User).save(user);
```
`config.verified` is used only to set `User.verified` and to write a `CUSTOMER_VERIFIED` history entry (later in the method) — it is **never** used to gate whether the external method may be attached to an existing account. So an unverified external email links to the victim's account just the same.
## Impact
Account takeover of any customer whose email address an attacker can present (unverified) via an external auth provider — read/modify the victim's orders, addresses, and PII, and place orders as them. The blast radius depends on the deployed `AuthenticationStrategy`(ies): strategies that don't strictly require a provider-verified email (or providers that don't guarantee email ownership) are directly exploitable.
## Reproduction (conceptual)
1. Victim has a native Vendure customer account `
[email protected]`.
2. Attacker authenticates through an external provider configured on the store, presenting `emailAddress =
[email protected]` with `verified` unset/false (depending on the strategy/provider).
3. `createCustomerAndUser` finds the victim's existing User by email and attaches the attacker's `ExternalAuthenticationMethod`.
4. Attacker logs in via that external method → authenticated as the victim.
## Suggested fix
Refuse to bind an external authentication method to a **pre-existing** account unless the email is provably verified, and prefer explicit, authenticated account-linking:
```ts
if (existingUser) {
if (!config.verified) {
// Do not silently link an unverified external identity to an existing account.
throw new EmailAddressConflictError(); // or require the user to link while logged in
}
user = existingUser;
}
```
Document clearly that an `AuthenticationStrategy` MUST only set `verified: true` for provider-verified emails, and that linking to existing accounts requires it.
