Android banking malware SlemBunk is part of a well-organized campaign

The Trojan is distributed through drive-by-download attacks that use multiple stages and non-malicious apps

An Android Trojan that targets mobile banking users has evolved into a sophisticated, persistent and hard-to-detect threat, suggesting that it is part of a well-organized attack campaign.

Researchers from security firm FireEye first documented the Trojan in December and named it SlemBunk. Once installed, it starts monitoring the processes running on the device and when it detects that a mobile banking app is launched, it displays a fake user interface on top of it to trick users into inputting their credentials.

The Trojan can spoof the user interfaces of apps from at least 31 banks from across the world and two mobile payment service providers.

The first variants of SlemBunk were distributed as rogue copies of legitimate apps through various third-party websites, but not Google Play. This meant that devices configured to only install apps from Google Play were not affected.

The latest versions, however, are distributed through drive-by download techniques, predominantly when visiting porn websites. Device owners are alerted that in order to view the videos on the site they need to update their Flash Player and an APK (Android application package) is offered for download.

"Unwary users, who are more eager to see the video than to consider what this app is really about, would readily accept what the website is saying, and happily install the app that claims to be a Flash update," the FireEye researchers said in a blog post Wednesday.

This would still require users to enable the installation of apps from unknown sources, which is disabled by default on Android devices.

The attack is more complicated than it appears at first glance, because the APK downloaded during this first stage does not contain any malicious functionality, making it hard for antivirus apps and even Android's built-in app scanner to detect it.

This "dropper" app is using a packing technique to hide some functions that generate code on the fly and save it to another temporary APK in the device's storage. This second APK is loaded into memory dynamically by the first app and is then deleted from the file system. It too is not explicitly malicious, but it contains the routine that downloads the final, malicious payload. 

The downloader app contacts a command-and-control server and receives the link for the actual SlemBunk APK and also its MD5 signature. The signature is used to verify that the downloaded file has not been tampered with or corrupted during transmission.

This chained attack, the first two steps of which are not directly malicious, is intended to make the attack more persistent, harder to detect and difficult to analyze, the FireEye researchers said. "Even if the malicious action of the SlemBunk payload were detected and removed, the more surreptitious downloader could periodically attempt to re-download the payload to the device."

The command-and-control infrastructure is also well thought out, using separate domain names for the payloads and the configuration data and administration panel.

"The use of a drive-by download to distribute the SlemBunk payload and the details of the CnC server communication suggest that this campaign is well-organized and continuing to evolve," the FireEye researchers said.

Join the PC World newsletter!

Error: Please check your email address.

Our Back to Business guide highlights the best products for you to boost your productivity at home, on the road, at the office, or in the classroom.

Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

Lucian Constantin

IDG News Service
Show Comments

Essentials

Lexar® JumpDrive® S57 USB 3.0 flash drive

Learn more >

Microsoft L5V-00027 Sculpt Ergonomic Keyboard Desktop

Learn more >

Mobile

Lexar® JumpDrive® S45 USB 3.0 flash drive 

Learn more >

Exec

Lexar® JumpDrive® C20c USB Type-C flash drive 

Learn more >

Audio-Technica ATH-ANC70 Noise Cancelling Headphones

Learn more >

Lexar® Professional 1800x microSDHC™/microSDXC™ UHS-II cards 

Learn more >

HD Pan/Tilt Wi-Fi Camera with Night Vision NC450

Learn more >

Budget

Back To Business Guide

Click for more ›

Most Popular Reviews

Latest News Articles

Resources

PCW Evaluation Team

Azadeh Williams

HP OfficeJet Pro 8730

A smarter way to print for busy small business owners, combining speedy printing with scanning and copying, making it easier to produce high quality documents and images at a touch of a button.

Andrew Grant

HP OfficeJet Pro 8730

I've had a multifunction printer in the office going on 10 years now. It was a neat bit of kit back in the day -- print, copy, scan, fax -- when printing over WiFi felt a bit like magic. It’s seen better days though and an upgrade’s well overdue. This HP OfficeJet Pro 8730 looks like it ticks all the same boxes: print, copy, scan, and fax. (Really? Does anyone fax anything any more? I guess it's good to know the facility’s there, just in case.) Printing over WiFi is more-or- less standard these days.

Ed Dawson

HP OfficeJet Pro 8730

As a freelance writer who is always on the go, I like my technology to be both efficient and effective so I can do my job well. The HP OfficeJet Pro 8730 Inkjet Printer ticks all the boxes in terms of form factor, performance and user interface.

Michael Hargreaves

Windows 10 for Business / Dell XPS 13

I’d happily recommend this touchscreen laptop and Windows 10 as a great way to get serious work done at a desk or on the road.

Aysha Strobbe

Windows 10 / HP Spectre x360

Ultimately, I think the Windows 10 environment is excellent for me as it caters for so many different uses. The inclusion of the Xbox app is also great for when you need some downtime too!

Mark Escubio

Windows 10 / Lenovo Yoga 910

For me, the Xbox Play Anywhere is a great new feature as it allows you to play your current Xbox games with higher resolutions and better graphics without forking out extra cash for another copy. Although available titles are still scarce, but I’m sure it will grow in time.

Featured Content

Latest Jobs

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?