New Android Trojan app exploits previously unknown flaws
By Lucian Constantin
A newly discovered Trojan program exploits previously unknown flaws in Android and borrows techniques from Windows malware in order to evade detection and achieve persistence on infected devices.
Security researchers from antivirus firm Kaspersky Lab named the new malicious application Backdoor.AndroidOS.Obad.a and labeled it the most sophisticated Android Trojan program to date.
The malware is designed to send SMS messages to premium-rate numbers and allows attackers to execute rogue commands on infected devices by opening a remote shell. Attackers can use the malware to steal any kind of data stored on compromised devices or to download additional malicious applications that can be installed locally or distributed to other devices over Bluetooth.
The Obad.a Trojan program makes heavy use of encryption and code obfuscation in order to hinder analysis efforts, Kaspersky researcher Roman Unuchek said Thursday in a blog post.
An intelligent bug
“Malware writers typically try to make the codes in their creations as complicated as possible, to make life more difficult for anti-malware experts,” the researcher said. “However, it is rare to see concealment as advanced as Odad.a’s in mobile malware.”
In addition to using encryption and code obfuscation techniques, the malware also exploits previously unknown bugs in Android and third-party software, Unuchek said.
For example, the malicious application exploits an error in a piece of software called DEX2JAR that’s used by malware analysts to convert Android application packages (APKs) into Java Archive (JAR) files.
“This vulnerability spotted by the cybercriminals disrupts the conversion of Dalvik bytecode into Java bytecode, which eventually complicates the statistical analysis of the Trojan,” Unuchek said.
The malware also abuses a bug in the way Android processes AndroidManifest.xml files. These files are found in every application and contain information about the application’s structure and launch parameters.
The Trojan program contains a specifically crafted AndroidManifest.xml that doesn’t conform to Google’s specification, but is still processed correctly by the Android OS, Unuchek said. This makes dynamic analysis of the malware extremely difficult, he said.
When first executed, Obad.a prompts users for device administrator privilege. Applications that gain this privilege can no longer be uninstalled through the regular apps menu until they are removed from the administrators list in the security settings menu.
The Obad.a malware exploits a previously unknown flaw in the Android OS in order to hide itself from the administrators list, leaving users unable to revoke the privilege and uninstall the app. “We have already informed Google about the Device Administrator vulnerability in Android,” Unuchek said.
In addition, on rooted devices, the malware tries to gain root privileges by executing the “su id” command, said Denis Maslennikov, a senior malware analyst at Kaspersky Lab, Friday via email. Like gaining administrative privileges, gaining root access requires user permission, he said.
“Backdoor.AndroidOS.Obad.a looks closer to Windows malware than to other Android Trojans, in terms of its complexity and the number of unpublished vulnerabilities it exploits,” Unuchek said.
The new Trojan program is distributed through SMS spam, but is not very widespread at the moment. According to detection statistics from Kaspersky Lab, installation attempts for Obad.a amounted to only 0.15 percent of the total number of malware infection attempts on mobile devices over a three-day period.
That said, Maslennikov believes that other Android malware threats will adopt advanced techniques like the ones used by this malware in the future. “We think that similar techniques are going to be more widespread very soon,” he said.