Authored by Dexter Shin
Abstract
Cybercriminals are consistently evolving their methods to bypass safety measures. Lately, the McAfee Cell Analysis Workforce found malware campaigns abusing .NET MAUI, a cross-platform growth framework, to evade detection. These threats disguise themselves as authentic apps, focusing on customers to steal delicate data. This weblog highlights how these malware function, their evasion methods, and key suggestions for staying protected.
Background
Lately, cross-platform cellular growth frameworks have grown in reputation. Many builders use instruments like Flutter and React Native to construct apps that work on each Android and iOS. Amongst these instruments, Microsoft offers a framework primarily based on C#, referred to as Xamarin. Since Xamarin is well-known, cybercriminals generally use it to develop malware. We have now beforehand discovered malware associated to this framework. Nonetheless, Microsoft ended help for Xamarin in Might 2024 and launched .NET MAUI as its substitute.
In contrast to Xamarin, .NET MAUI expands platform help past cellular to incorporate Home windows and macOS. It additionally runs on .NET 6+, changing the older .NET Commonplace, and introduces efficiency optimizations with a light-weight handler-based structure as a substitute of customized renderers.
As know-how evolves, cybercriminals adapt as nicely. Reflecting this pattern, we lately found new Android malware campaigns developed utilizing .NET MAUI. These Apps have their core functionalities written completely in C# and saved as blob binaries. Which means in contrast to conventional Android apps, their functionalities don’t exist in DEX information or native libraries. Nonetheless, many antivirus options deal with analyzing these parts to detect malicious habits. Because of this, .NET MAUI can act as a kind of packer, permitting malware to evade detection and stay lively on units for a very long time.
Within the following sections, we’ll introduce two Android malware campaigns that use .NET MAUI to evade detection. These threats disguise themselves as authentic companies to steal delicate data from customers. We’ll discover how they function and why they pose a major threat to cellular safety.
Am I protected?
McAfee Cell Safety already detects all of those apps as Android/FakeApp and protects customers from these threats. For extra details about our Cell Product, go to McAfee Cell Safety.
Technical Findings
Whereas we discovered a number of variations of those malicious apps, the next two examples are used to reveal how they evade detection.
First off, the place are customers discovering these malicious apps? Usually, these apps are distributed by way of unofficial app shops. Customers are sometimes directed to such shops by clicking on phishing hyperlinks made out there by untrusted sources on messaging teams or textual content messages. Because of this we suggest at McAfee that customers keep away from clicking on untrusted hyperlinks.
Instance 1: Faux Financial institution App
The first faux app we discovered disguises itself as IndusInd Financial institution, particularly focusing on Indian customers. When a person launches the app, it prompts them to enter private and monetary particulars, together with their title, cellphone quantity, e mail, date of start, and banking data. As soon as the person submits this knowledge, it’s instantly despatched to the attacker’s C2 (Command and Management) server.
Determine 1. Faux IndusInd Financial institution app’s display requesting person data
As talked about earlier, this isn’t a standard Android malware. In contrast to typical malicious apps, there are not any apparent traces of dangerous code in the Java or native code. As a substitute, the malicious code is hidden inside blob information positioned contained in the assemblies listing.
Determine 2. Blob accommodates malicious code
The next code snippet reveals how the app collects and transmits person knowledge to the C2 server. Based mostly on the code, the app constructions the required data as parameters earlier than sending it to the C2 server.
Determine 3. C# code chargeable for stealing person knowledge and sending it to the C2 server
Instance 2: Faux SNS App
In distinction to the first faux app, this second malware is much more tough for safety to investigate. It particularly targets Chinese language-speaking customers and makes an attempt to steal contacts, SMS messages, and pictures from their units. In China, the place entry to the Google Play Retailer is restricted, such apps are sometimes distributed by way of third-party web sites or different app shops. This permits attackers to unfold their malware extra simply, particularly in areas with restricted entry to official app shops. 
Determine 4. Distribution website and faux X app focusing on Chinese language-speaking customers
One of many key methods this malware makes use of to stay undetected is multi-stage dynamic loading. As a substitute of straight embedding its malicious payload in an simply accessible format, it encrypts and masses its DEX information in three separate levels, making evaluation considerably harder.
Within the first stage, the app’s essential exercise, outlined in AndroidManifest.xml, decrypts an XOR-encrypted file and masses it dynamically. This preliminary file acts as a loader for the subsequent stage. Within the second stage, the dynamically loaded file decrypts one other AES-encrypted file and masses it. This second stage nonetheless doesn’t reveal the core malicious habits however serves as one other layer of obfuscation. Lastly, within the third stage, the decrypted file accommodates code associated to the .NET MAUI framework, which is then loaded to execute the primary payload.
Determine 5. Multi-stage dynamic loading
The principle payload is in the end hidden inside the C# code. When the person interacts with the app, akin to urgent a button, the malware silently steals their knowledge and sends it to the C2 server.
Determine 6. C# code chargeable for stealing photos, contacts, and SMS knowledge
Past multi-stage dynamic loading, this malware additionally employs extra methods to make evaluation harder. One approach is manipulating the AndroidManifest.xml file by including an extreme variety of pointless permissions. These permissions embody giant quantities of meaningless, randomly generated strings, which may trigger errors in sure evaluation instruments. This tactic helps the malware evade detection by disrupting automated scanners and static evaluation.
Determine 7. AndroidManifest.xml file with extreme random permissions
One other key approach is encrypted socket communication. As a substitute of utilizing customary HTTP requests, that are simpler to intercept, the malware depends on TCP socket connections to transmit knowledge. This method makes it tough for conventional HTTP proxy instruments to seize community visitors. Moreover, the malware encrypts the info earlier than sending it, which means that even when the packets are intercepted, their contents stay unreadable.
Yet one more necessary side to notice is that this malware adopts numerous themes to draw customers. Along with the faux X app, we additionally found a number of relationship apps that use the identical methods. These apps had totally different background photos however shared the identical construction and performance, indicating that they have been doubtless created by the identical developer because the faux X app. The continual emergence of comparable apps means that this malware is being extensively distributed amongst Chinese language-speaking customers.
Determine 8. Varied faux apps utilizing the identical approach
Suggestions and Conclusion
The rise of .NET MAUI-based malware highlights how cybercriminals are evolving their methods to keep away from detection. Among the methods described embody:
- hiding code blobs inside assemblies
- multi-stage dynamic loading
- encrypted communications
With these evasion methods, the threats can stay hidden for lengthy intervals, making evaluation and detection considerably more difficult. Moreover, the invention of a number of variants utilizing the identical core methods means that such a malware is turning into more and more frequent.
Customers ought to at all times be cautious when downloading and putting in apps from unofficial sources, as these platforms are sometimes exploited by attackers to distribute malware. That is particularly regarding in nations like China, the place entry to official app shops is restricted, making customers extra susceptible to such threats.
To maintain up with the fast evolution of cybercriminal techniques, customers are strongly suggested to put in safety software program on their units and hold it updated always. Staying vigilant and making certain that safety measures are in place can assist shield in opposition to rising threats. By utilizing McAfee Cell Safety, customers can improve their gadget safety and detect threats associated to such a malware in real-time.
Glossary of Phrases
Indicators of Compromise (IOCs)
APKs:
C2:
- tcp[://]120.27.233.135:1833
- https[://]onlinedeskapi.com
