![]() ![]() Where possible, Canary's Push notifications server leverages OAuth tokens instead of credentials for obtaining account access. The advantage of using a Push notifications server is that an IDLE connection to the email server is maintained reliably by the server instead of the user's device, and as a result the user is notified of new incoming mail instantly and reliably, regardless of whether the app is in the foreground, background, is in suspended state, or has been force-quit. This is why Canary offers a second method for checking for new mail, called Push, since it relies on a Push notifications server. However, since both iOS and Android do not guarantee access to CPU and network resources in a variety of situations, including when the app is in a suspended state or has been force-quit by the user, the delay in receiving notifications for new mail can vary considerably and unpredictably. ![]() Unfortunately, this method leads to some delay between the arrival of the new email, and the user being notified of the same, typically under ~15 minutes since the email server can only be queried periodically, and not continuously. The advantage of using Fetch notifications is that new mail is fetched directly by the user's own device and all data, including account credentials, is stored locally only. One is on-device Fetch, where Canary periodically queries the email server to check for new mail. ![]() To workaround these restrictions, Canary offers two methods for checking new mail on mobile. For example, an app cannot access CPU and network resources when it is in a suspended state or has been force-quit by the user, or due to other restrictions imposed by the OS (eg low power mode). On mobile, it is impossible to reliably maintain an open IDLE connection to the email server due to several limitations. This is how most desktop email clients, such as Canary for macOS, check for new mail. This vulnerability was verified in versions 3.20 and 3.21 of the software.The standard method for checking for new incoming emails as recommended by the IMAP specification is to maintain an open IDLE connection to the email server. While testing Canary Mail with the IMAP STARTTLS setting, CENSUS found that the iOS and MacOS versions of the software would happily connect to a fake IMAP service introduced by a man-in-the-middle attacker, as they performed no certificate validation. A patch for the library is publicly available, however this has not been incorporated yet into an official library release.ĬENSUS performed a functional security test to a number of mail clients, looking for possible vulnerabilities related to man-in-the-middle attacks. The same vulnerability also affects other software that are based on the MailCore2 library (including version 0.6.4). ![]() CENSUS strongly recommends to iOS and MacOS users of the Canary Mail software to update to version 3.22, as this version carries a fix for the aforementioned vulnerability. This vulnerability allows man-in-the-middle attackers to collect a victim user's email credentials (while these are communicated to the IMAP service), to access email messages and perform other IMAP actions to the victim account, but also to modify email messages while in-transit to Canary Mail. Improper Certificate Validation ( CWE-295)ĬENSUS identified that the Canary Mail software in versions 3.20 and 3.21 (and possibly previous versions) is missing a certificate validation check when performing an IMAP connection configured with STARTTLS. Canary Mail and MailCore2 library missing certificate validation check on IMAP STARTTLS CENSUS ID:Ĭanary Mail for iOS and MacOS versions 3.20 and 3.21, MailCore2 library version 0.6.4 ![]()
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