Remote exploitation of a man-in-the-disk vulnerability in WhatsApp (CVE-2021-24027)
CENSUS has been investigating for some time now the exploitation potential of Man-in-the-Disk (MitD) [01] vulnerabilities in Android. Recently, CENSUS identified two such vulnerabilities in the popular WhatsApp messenger app for Android [34]. The first of these was possibly independently reported to Facebook and was found to be patched in recent versions, while the second one was communicated by CENSUS to Facebook and was tracked as CVE-2021-24027 [33]. As both vulnerabilities have now been patched, we would like to share our discoveries regarding the exploitation potential of such vulnerabilities with the rest of the community.
WhatsApp exposure of TLS 1.2 cryptographic material to third party apps
| CENSUS ID: | CENSUS-2021-0002 |
| CVE ID: | CVE-2021-24027 |
| Affected Products: | WhatsApp Messenger for Android, versions prior to 2.21.4.18 |
| Class: | Exposure of Sensitive Information to an Unauthorized Control Sphere (CWE-497) |
| Discovered by: | Chariton Karamitas |
CENSUS identified that versions prior to 2.21.4.18 of WhatsApp for Android allowed third party apps to access WhatsApp TLS 1.2 cryptographic material, as this was stored in "app-specific external storage". On Android 9 and previous versions of Android, the material is exposed to any third party app that bears the READ_EXTERNAL_STORAGE or WRITE_EXTERNAL_STORAGE permission. On Android 10 a malicious app would also require the requestLegacyExternalStorage attribute to access the files. Through the installation of a malicious app, or alternatively, through the exploitation of a vulnerable app (or Android component) that resides on a WhatsApp user's mobile device, remote actors were able to control the victim user's TLS session cryptographic secrets and could thus perform Man-in-The-Middle attacks to WhatsApp communications. Research has shown that exploitation of this vulnerability can lead to remote code execution on the victim device. CENSUS strongly recommends updating WhatsApp to version 2.21.4.18 or greater. This is a serious vulnerability which could be abused for surveillance purposes.
Canary Mail and MailCore2 library missing certificate validation check on IMAP STARTTLS
| CENSUS ID: | CENSUS-2021-0001 |
| CVE ID: | CVE-2021-26911 |
| Affected Products: | Canary Mail for iOS and MacOS versions 3.20 and 3.21, MailCore2 library version 0.6.4 |
| Class: | Improper Certificate Validation (CWE-295) |
| Discovered by: | Rayd Debbas |
CENSUS 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. 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. 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. The same vulnerability also affects other software that are based on the MailCore2 library (including version 0.6.4). A patch for the library is publicly available, however this has not been incorporated yet into an official library release.
The Known Beacons Attack (34th Chaos Communication Congress)
The recent key reinstallation attacks (KRACK) against the WPA2 protocol revealed how an adversary can easily eavesdrop, and in some cases tamper, a Wi-Fi connection secured by the WPA2 protocol. At the same time, Wi-Fi automatic association attacks achieve a similar result (man-in-the-middle position) not by attacking the WPA2 protocol directly but by enforcing Wi-Fi clients to join a rogue Access Point.