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Researchers say mobile malware purveyors have been abusing a bug in the Google Android platform that lets them sneak malicious code into mobile apps and evade security scanning tools. Google says it has updated its app malware detection mechanisms in response to the new research.
At issue is a mobile malware obfuscation method identified by researchers at ThreatFabric, a security firm based in Amsterdam. Aleksandr Eremin, a senior malware analyst at the company, told KrebsOnSecurity they recently encountered a number of mobile banking trojans abusing a bug present in all Android OS versions that involves corrupting components of an app so that its new evil bits will be ignored as invalid by popular mobile security scanning tools, while the app as a whole gets accepted as valid by Android OS and successfully installed.
“There is malware that is patching the .apk file [the app installation file], so that the platform is still treating it as valid and runs all the malicious actions it’s designed to do, while at the same time a lot of tools designed to unpack and decompile these apps fail to process the code,” Eremin explained.
Eremin said ThreatFabric has seen this malware obfuscation method used a few times in the past, but in April 2023 it started finding many more variants of known mobile malware families leveraging it for stealth. The company has since attributed this increase to a semi-automated malware-as-a-service offering in the cybercrime underground that will obfuscate or “crypt” malicious mobile apps for a fee.
Eremin said Google flagged their initial May 9, 2023 report as “high” severity. More recently, Google awarded them a $5,000 bug bounty, even though it did not technically classify their finding as a security vulnerability.
“This was a unique situation in which the reported issue was not classified as a vulnerability and did not impact the Android Open Source Project (AOSP), but did result in an update to our malware detection mechanisms for apps that might try to abuse this issue,” Google said in a written statement.
Google also acknowledged that some of the tools it makes available to developers — including APK Analyzer — currently fail to parse such malicious applications and treat them as invalid, while still allowing them to be installed on user devices.
“We are investigating possible fixes for developer tools and plan to update our documentation accordingly,” Google’s statement continued.
Image: ThreatFabric.
According to ThreatFabric, there are a few telltale signs that app analyzers can look for that may indicate a malicious app is abusing the weakness to masquerade as benign. For starters, they found that apps modified in this way have Android Manifest files that contain newer timestamps than the rest of the files in the software package.
More critically, the Manifest file itself will be changed so that the number of “strings” — plain text in the code, such as comments — specified as present in the app does match the actual number of strings in the software.
One of the mobile malware families known to be abusing this obfuscation method has been dubbed Anatsa, which is a sophisticated Android-based banking trojan that typically is disguised as a harmless application for managing files. Last month, ThreatFabric detailed how the crooks behind Anatsa will purchase older, abandoned file managing apps, or create their own and let the apps build up a considerable user base before updating them with malicious components.
ThreatFabric says Anatsa poses as PDF viewers and other file managing applications because these types of apps already have advanced permissions to remove or modify other files on the host device. The company estimates the people behind Anatsa have delivered more than 30,000 installations of their banking trojan via ongoing Google Play Store malware campaigns.
Google has come under fire in recent months for failing to more proactively police its Play Store for malicious apps, or for once-legitimate applications that later go rogue. This May 2023 story from Ars Technica about a formerly benign screen recording app that turned malicious after garnering 50,000 users notes that Google doesn’t comment when malware is discovered on its platform, beyond thanking the outside researchers who found it and saying the company removes malware as soon as it learns of it.
“The company has never explained what causes its own researchers and automated scanning process to miss malicious apps discovered by outsiders,” Ars’ Dan Goodin wrote. “Google has also been reluctant to actively notify Play users once it learns they were infected by apps promoted and made available by its own service.”
The Ars story mentions one potentially positive change by Google of late: A preventive measure available in Android versions 11 and higher that implements “app hibernation,” which puts apps that have been dormant into a hibernation state that removes their previously granted runtime permissions.
Google’s Android operating system has been a boon for the average consumer. No other operating system has given so much freedom to developers and hardware manufacturers to make quality devices at reasonable prices. The number of Android phones in the world is astounding. That success comes with a price, however.
A recent report from our own McAfee Mobile Research team has found malicious apps with hundreds of thousands of downloads in the Google Play store. This round of apps poses as simple wallpaper, camera filters, and picture editing, but they hide their nature till after they’ve been installed on your device.
Figure 1. Infected Apps on Google Play
On the bright side, Google Play performs a review for every app to ensure that they are legitimate, safe, and don’t contain malware before they’re allowed on the Play store. However, enterprising criminals regularly find ways to sneak malware past Google’s security checks.
Figure 2. Negative reviews on Google Play
When developers upload their apps to the Play store for approval, they have to send supporting documents that tell Google what the app is, what it does and what age group it’s intended for. By sending Google a “clean” version of their app, attackers can later get their malicious code into the store via a future update where it sits and waits for someone to download it. Once installed, the app contacts a remote server, controlled by the attackers, so it can download new parts of the app that Google has never seen. You can think of it as a malware add-on pack that installs itself on your device without you realizing it. By contacting their own server for the malware files, attackers sneak around Google security checks and can put anything they want on your device.
The current round of malware we’re seeing hijack your SMS messages so they can make purchases through your device, without your knowledge. Through a combination of hidden functionality and abuse of permissions like the ability to read notifications, that simple looking wallpaper app can send subscription requests and confirm them as if it were you. These apps will regularly run up large bills through purchasing subscriptions to premium rate services. The more troubling part is how they can read any message that you receive, possibly exposing your personal information to attackers.
To start, a comprehensive and cross-platform solution like McAfee Total Protection can help detect threats like malware and alerts you if your devices have been infected. I’d also like to share some tips our Research team has shared with me.
Before you hit that install button, take a good look at an app’s reviews. Do they look like they were written by real people? Do the account names of the reviewers make sense? Are people leaving real feedback, or are the majority of comments things like, “Works great. Loved it.” with no other information?
Scammers can easily generate fake reviews for an app to make it look like people are engaging with the developers. Look out for vague reviews that don’t mention the app or what it does, nothing but five-star reviews, and generic sounding account names like, “girl345834”. They’re probably bots, so be wary.
Search for the app developers’ company and see if they have a website. Having a website doesn’t guarantee an app is legitimate, but it’s another good indicator of how trustworthy a company’s app is. Through their website, you should be able to find out where their team is based, or at least some personal information about the company. If they’re hiding that information, or there’s no site at all, that might be a good sign to try a different app.
A lot of malicious apps offer features that your phone already provides, like a flashlight or photo viewer. Unless there’s a very specific reason why you need a separate app to do something your device already does, it’s not recommended to use a third-party app. Especially if it’s free.
App permissions must be clearly stated on the app’s page in order to get into the Google Play store. They’re found near the bottom of the page, along with developer information. Check the permissions every app asks for before you install it and ask yourself if they make sense. For example, a photo editor doesn’t need access to your contacts list, and wallpapers don’t need to have access to your location data. If the permissions don’t make sense for the type of app, steer clear.
Mobile devices are vulnerable to malware and viruses, just like your computer. By installing McAfee protection to your mobile device, you can secure your mobile data, protect your privacy, and even find lost devices.
Android is one of the most popular operating systems on the planet, which means the rewards for creating malware for Android devices are well worth it. It’s unlikely that Android malware is going away any time soon, so staying safe means being cautious with the things you install on your devices.
You can protect yourself by installing McAfee Total Protection on your mobile device and reading the permissions apps ask for when you install them. There’s no good reason for a wallpaper app to have SMS permissions, but that request should ring some alarm bells that something isn’t right and stop you from installing it.
The post Fraudulent Apps that Automatically Charge you Money Spotted in Google Play appeared first on McAfee Blogs.
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