An issue was discovered in cyrus-imapd in Cyrus IMAP through 3.12.2. There is an XAPPLEPUSHSERVICE folder existence oracle and push hijack. An authenticated IMAP user could probe for the existence of arbitrary mailboxes on other users' accounts via the XAPPLEPUSHSERVICE command and then create Apple Push Notification Service notifications for new mail in those mailboxes to their own APNS device. This did not leak any data about the content of mailboxes. Instead, a "mailbox has changed" notice would be pushed when the mailbox modseq changed.