Craft is a content management system (CMS). Prior to 5.9.0-beta.2 and 4.17.0-beta.2, the actionSendActivationEmail() endpoint is accessible to unauthenticated users and does not require a permission check for pending users. An attacker with no prior access can trigger activation emails for any pending user account by knowing or guessing the user ID. If the attacker controls the target user’s email address, they can activate the account and gain access to the system. This vulnerability is fixed in 5.9.0-beta.2 and 4.17.0-beta.2.
Affected: Packagist: craftcms/cms
The `actionSendActivationEmail()` endpoint is accessible to unauthenticated users and does not require a permission check for pending users. An attacker with no prior access can trigger activation emails for any pending user account by knowing or guessing the user ID. If the attacker controls the target user’s email address, they can activate the account and gain access to the system.
The vulnerability is not that anonymous access exists - there’s a legitimate use case for it. The vulnerability is that the endpoint accepts arbitrary `userId` parameters without verifying ownership.
Craft CMS allows public user registration. When a user registers but doesn’t receive their activation email (spam filter, typo correction, etc.), they need a way to request a resend. This is why `send-activation-email` is in the `allowAnonymous` array - it’s intentional self-service functionality.
### The Security Gap
The endpoint accepts `userId` as the identifier: ```php $userId = $this->request->getRequiredBodyParam('userId'); ```
This allows any visitor to trigger activation emails for any pending user, not just their own registration.
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## Background
When administrators create new user accounts in Craft CMS, users are created in a “pending” state until they activate their account via an emailed link. The `actionSendActivationEmail()` function sends (or resends) this activation email.
**Expected Behavior:** Anonymous users should only be able to resend activation emails for their own…