Although the Hacking Team leak took place several months ago, the impact of this data breach—where exploit codes were made public and spurred a chain of attacks—can still be felt until today. We recently spotted malicious Android apps that appear to use an exploit found in the Hacking Team data dumps. The apps, found in certain websites, could allow remote attackers to gain root privilege when successfully exploited. Mobile devices running on Android version 4.4 (KitKat) and below, which account for nearly 57% of total Android devices, are susceptible to attacks that may abuse this flaw.

The attack details

Based on our analysis, the malicious apps contain an exploit binary called reed , which employs the Hacking Team’s kernel_waiter_exploit. The latter exploit takes advantage of the “TowelRoot” vulnerability (CVE-2014-3153) to implant a root backdoor on the device. TowelRoot is a relatively old vulnerability in Linux that has been patched in 2014.

With this root backdoor, the malware fetches the latest payload executed as root privilege from its command-and-control (C&C) server, hxxps://remote[.]ibtubt[.]com/phone/.

Figure 1. Exploit code from the Hacking Team leak

The cyber crooks behind this attack embedded the exploit code in several gaming and launcher apps hosted in the site, hxxp://risechen[.]b0[.]upaiyun[.]com. Some examples of malicious apps include Maria’s coffie shop, 酷酷斗地主, iLauncher, One Launcher, and Launcher IP Style 6s among others. We observed at least 88 apps with this exploit. Currently, we haven’t seen any of these malicious apps in third-party app stores.

Figure 2. Sample malicious gaming app that has exploit code

Interestingly, we found one of these launcher apps (known as Motion Launcher) in Google Play, albeit only its lower, non-malicious version (1.0.62_how_1504221926). The higher version (1.0.78_how_1508051719) with malicious code was signed with the same certificate as the app version in Play Store. This indicates that both apps were created by the same developer. Both codes of the apps bore the same author’s name: Ren Fei. We surmise that due to Google’s review process, the malicious version of the said app failed to get online.

Figure 3. Details of the non-malicious version of the launcher app on Google Play

Figure 4. App signature of legitimate vis-à-vis malicious apps shows identical developer

Trend Micro detects the exploit binary as ANDROIDOS_TOWELROOT.A. Based on our Smart Protection Network data, majority of the affected users reside in Asia Pacific region.

Figure 5. Global distribution of malicious apps with TowelRoot installations

Piecing it together

We tried to piece together the details mentioned above to understand better how the attack works. We started looking into the site (hxxp://risechen[.]b0[.]upaiyun[.]com), where the apps are hosted. Given that the CDN site, upaiyun.com, is a legitimate cloud service provider, it appears that these malicious apps are served by abusing the said service. We also found out that users can be directed to this site (upaiyun.com) when they download an Android application package (APK) via malicious sites or through recommended apps from other apps. We already notified the upaiyun regarding this incident.

The said apps also access this malicious app store, hxxp://android[.]kukool[.]net/api/android/appstore/v2/realtime, which belongs to a gaming company in China. This company distributes normal apps to third party stores or even to Google Play Store. These non-malicious apps via app recommendation push malicious apps from the above mentioned malicious app store to users.

Through this attack, cybercriminals can use TowelRoot to plant backdoor onto the mobile devices. This can also download any malicious code from the C&C server and execute it at root privilege thus compromising the device’s security. To a certain degree, this can be tagged as a sort of remote control malware because once an outdated device is infected, it becomes part of the bot. Some variants added functions such as device admin lock and app hiding for ‘anti-uninstall’ purposes.

Mobile devices with the latest Android OS (Lollipop and above) are not affected by this attack. Even though the logical step would be for users to update their Android OS, it’s highly improbable due to the challenges that mobile device fragmentation pose. However, users need not to fret as scanning unknown source app with security apps like Trend Micro Mobile Security Personal Edition and Mobile Security Solutions can detect malicious apps and blocks malicious URLs related to this attack. If the device is already infected, firmware flash is necessary to remove the backdoor.

The malicious app names, SHA1 hashes and URLs related to this threat can be found in this appendix.