Froxlor: Authenticated customers can read other customers' allowed sender aliases

Summary

An authenticated customer can read other customers' allowed sender aliases from Froxlor's sender-delete confirmation page when mail.enable_allow_sender is enabled. customer_email.php loads allowed_sender by global auto-increment senderid alone, so a customer can enumerate foreign sender alias IDs and make Froxlor disclose those values in the confirmation dialog for the attacker's own mailbox.

Details

The vulnerable read lives in customer_email.php:

$senderid = Request::any('senderid', 0);
...
$sel_stmt = Database::prepare("SELECT `allowed_sender` FROM `" . TABLE_MAIL_SENDER_ALIAS . "` WHERE `id` = :sid");
$sender_data = Database::pexecute_first($sel_stmt, ['sid' => $senderid]);

HTML::askYesNo('email_reallydelete_sender', $filename, [
    'id' => $id,
    'senderid' => $senderid,
    'page' => $page,
    'domainid' => $email_domainid,
    'action' => $action
], $idna_convert->decode($result['email_full']) . ' -> ' . $sender_data['allowed_sender']);

The query does not scope senderid to the current customer or to the mailbox being edited. mail_sender_aliases.id is a global AUTO_INCREMENT primary key:

CREATE TABLE `mail_sender_aliases` (
  `id` int(11) NOT NULL auto_increment,
  `email` varchar(255) NOT NULL,
  `allowed_sender` varchar(255) NOT NULL,
  PRIMARY KEY  (`id`)
)

That makes sender alias IDs enumerable. A customer who owns any mailbox with sender-alias management enabled can request the delete-confirmation page for their own mailbox while supplying foreign senderid values. Froxlor then renders the foreign allowed_sender string in the confirmation prompt.

Proof of Concept

Verified against Froxlor 2.3.6 on a fresh test install with mail.enable_allow_sender=1.

1. Create two customers, victim and attacker.
2. Give each customer one mailbox.
3. Add a sender alias for the victim mailbox:

[email protected] -> [email protected]