Digital attackers uploaded 17 versions of the Joker malware family to Google’s Play Store in September 2020 as part of an ongoing effort to target Android users.

How the Attackers Bypassed Google’s Vetting Process

The Zscaler ThreatLabZ research team found on Sept. 24, 2020, that digital attackers had concealed the Joker malware versions in applications ranging from PDF scanners to Android keyboards and photo collage programs to translators.

In its study of the malicious apps, the firm found that digital attackers used one of three techniques on each occasion to evade detection by Google’s vetting systems.

The first scenario involved the download of the Joker malware payload from a URL sent over by the attackers’ command-and-control (C&C) server. The apps did this by using string obfuscation to conceal the C&C address in its code.

As for the second scenario, the malicious app dispensed with a C&C address and opted for a stager payload URL encoded in its code. The malware downloaded the stager payload in the form of an Android Package or a Dalvik executable file. This stager then retrieved the final payload URL, downloaded the payload and ran it.

For the third and final scenario, the infected app contacted its C&C server to retrieve a stage one payload URL and download the payload. This payload then obtained a stage two payload that functioned exactly as the first. That payload included a hardcoded URL for downloading the final payload.

At that point, the Joker malware got to work. It stole SMS messages and contact lists and signed the victim up for premium wireless application protocol services.

Those apps had garnered about 120,000 downloads at the time Zscaler discovered them.

Zscaler’s researchers notified the Google Android Security team about the malicious apps. Because of this, Google’s personnel removed the apps from the Play Store.

Other Recent Attacks Involving Joker Malware

The malware attack described above wasn’t the first time in 2020 that Joker made headlines. Back in February, Check Point Research found that a few new samples of the spyware and premium dialer family had infiltrated Google’s Play Store. Those samples garnered more than 130,000 downloads at the time they were found. They all appeared on Check Point’s radar at the same time as a new click malware family called Haken.

Just a few months after, Check Point once again detected Joker samples hiding in the Play Store. This time, however, they spotted the malware using an old trick from the PC threat world — concealing a dynamically loaded hex file — to evade Google’s detection. A couple of months later, Pradeo found six more apps infected with the malware. Then, at the end of September, Zimperium reported on the discovery of 64 Joker variants within the span of less than a month.

How to Defend Against Mobile Malware

Organizations can help defend against types of malware like Joker by abiding by mobile security best practices. For instance, they can use their comprehensive vulnerability management programs to keep all mobile devices up to date and to limit app installations to trusted developers on official marketplaces. Security teams can enshrine these practices into their organization’s security policies to augment those measures. They also can use ongoing security awareness training to educate the workforce about the importance of following those guidelines.

Simultaneously, organizations can consider using advanced security solutions that use AI to spot threats that prey upon mobile devices and/or other connected assets in an attempt to infiltrate the corporate network.

More from News

Abuse of Privilege Enabled Long-Term DIB Organization Hack

From November 2021 through January 2022, the Cybersecurity and Infrastructure Security Agency (CISA) responded to an advanced cyberattack on a Defense Industrial Base (DIB) organization’s enterprise network. During that time frame, advanced persistent threat (APT) adversaries used an open-source toolkit called Impacket to breach the environment and further penetrate the organization’s network. Even worse, CISA reported that multiple APT groups may have hacked into the organization’s network. Data breaches such as these are almost always the result of compromised endpoints…

Costa Rica State of Emergency Declared After Ransomware Attacks

In late April, after weeks of major ransomware attacks, Costa Rica declared a state of emergency. Newly-elected President Rodrigo Chaves took this measure, usually reserved to deal with natural disasters, to free up the government to react more decisively to the incident. The Russian-based Conti gang has claimed they launched the attack. Meanwhile, the U.S. Department of State offered a $10 million reward for information that leads to finding anyone holding a key leadership role in the Conti gang. The…

Ransomware-as-a-Service Transforms Gangs Into Businesses

Malware-as-a-Service is getting easier and easier to access, according to a recent threat report. Self-named the ‘Eternity Project’, this cyber threat group offers services from a Tor website and on their Telegram channel. They sell a wide variety of malware in an organized fashion, including stealer, clipper, worm, miner, ransomware and distributed-denial-of-service bot services. This alarms many security professionals. With Eternity, even inexperienced cyber criminals can target victims with a customized threat offering. Eternity sells malware for $90 to $490.…

UK Health System Email Accounts Hijacked to Steal Microsoft Logins

Last summer, I noticed password reset notices in my email account that I didn’t send. I quickly realized that I was the victim of an account takeover. This happens when someone illegally gains access to your account, typically through compromised credentials. I changed my email password right away and learned that my passwords to other accounts had already been changed. To make cleanup even more fun, I found out that the attackers had created new accounts using my credentials. Account…