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A New MSBuild Fileless Malware Campaign in Which Threat Actors Used MSBuild to Deliver RATs
Another serious malware distribution campaign has been launched on the internet targeting the Windows system. The most disturbing fact is most antivirus engines failed to detect the malware. MSBuild Fileless Malware Campaign was launched last month in which Threat Actors used Microsoft’s MSBuild tool as a stealth weapon to deliver Remote Access Trojans and password-stealing malware known as RedLine stealer.
How Is This MSBuild Fileless Malware Campaign Designed to Deliver The Malware?
Infection flow chain
Threat actors have abused Microsoft’s MSBuild (A tool used for building apps) to deliver the malware filelessly. Primarily three malware were seen in the campaign: RemcosRAT, Quasar, and RedLine stealer in the campaign.
RemcosRAT (aka Remote Control and Surveillance software) grants full access to the remote attacker, its features ranging from capturing keystrokes and recording microphones and webcams to executing arbitrary commands. Quasar is an open-source .NET-based RAT that can be capable of keylogging and password-stealing with many other capabilities. RedLine stealer is a malware program that can harvest credentials from browsers, VPNs, and messaging clients.
It has been seen that threat actors have weaponized the MSBuild.proj file by embedding encoded executables and shellcode in it. At this point in time, we still don’t know how the malware is getting distributed. However, we have found that the malware was hosted on a Russian image hosting site joxi[.]net. Visit here to learn more about it.
Why Threat Actors Used MSBuild to Carry Out the MSBuild Fileless Malware Campaign?
If you don’t know about MSBuild, it is a development tool mostly used for building applications for the Windows platform. Specifically when Visual Studio is not present in the system. MSBuild uses XML projects which store the complete details required to compel the whole project. There is a “UsingTask” element in the configuration file, which defines the task that will be compiled by the MSBuild tool. In addition to the “UsingTask” element, MSBuild has an inline task feature that enables the code to be compiled by MSBuild and executed in memory. This feature to execute the code in memory has created an excellent opportunity for threat actors to use MSBuild in this MSBuild fileless malware campaign.
What Is Fileless Malware? And, Why Is It Important to Know About It?
Fileless malware is a type of malware that uses a legitimate program to load the malware into memory. Unlike traditional malware, fileless malware does not require the attacker to drop a code on a target’s system for execution. This technique has made it hard to detect. In experimental conditions, most antivirus engines either failed to detect the fileless malware or flag low severity detection.
Characteristics of Fileless Malware:
Abuse legitimate applications that are already on the targeted system
No identifiable code or signature that traditional AV solutions could detect
No particular behavior that heuristics scanners could identify
Memory-based: lives in system memory
It uses built-in processes that are in the operating system.
It can be embedded with other types of malware.
May reside in the environment despite sandboxing measures.
RemcosRAT
Remcos RAT Review – The Most Advanced Remote Access Tool
We thanks for Breaking Security for creating such awesome video content on Remcos RAT
Remcos is a commercial software created by Breaking Security. It has both community and as well as a free edition. The application has been created to support remote administrators to perform remote control, remote admin, remote anti-theft, remote support, and pen-testing. However, Remcos has often been used by threat actors for malicious purposes. The software is written in C++ and enables full access to the remote machine. Some of its features include:
Remote Scripting | Notifications |
Webcam Capture | Remote Command Line |
Clear Logins | Remote Chat |
File Manager | Remote Input |
Microphone Capture | SOCKS Proxy |
Keylogger | Login Cleaner |
Screen Logger | Local Utilities |
Browser History | Registry Editor |
Password Recovery | Visibility mode |
Remcos features table
RedLine Stealer
As the name says, RedLine Stealer is an open-source tool used for password harvesting. It is written in .NET and has been observed stealing credentials including:
Chrome | GameLauncher for Steam |
Filezilla | Guarda |
Gecko | Jaxx |
Armory | Metamask |
Atomic | Monero |
Coinom | OpenVPN |
DesktopMessenger for Telegram | NordVPN |
Discord | ProtonVPN |
Electrum | Tronlink |
Ethereum | Yoroi |
RedLine Stealer’s list
How to Prevent the MSBuild Fileless Malware Campaign?
The main strength of fileless malware is its stealthy nature. This malware is tough to detect. Legacy AV, sandboxing, and machine learning methods will fail to detect fileless malware attacks. Security engineers can’t merely ignore stating these are difficult to detect. We will list some techniques that could work as a game-changer in preventing fileless malware.
Search for IOAs (Indicator of Attack): IOAs include signs such as code execution, lateral movements, and behavioral actions. IOAs don’t tell how the attack is being carried out. Instead, it talks about the signs of in-progress attacks.
Keep the systems up to date: Never miss applying the new upgrades or patches.
Remove unwanted services: Disable unwanted ports, enforce to use of only secure network protocols, and remove unused applications from the system.
Fix latest vulnerabilities: Run the periodic VA scan and fix all vulnerabilities, incredibly remote execution vulnerabilities.
Harden the system: Close all the configuration gaps and make the system more secure.
Defense-in-Depth strategy: Don’t trust a single product. Deploy multiple layers of defense and use multiple different products for the defense.
Cybersecurity training & awareness: Host training programs and create awareness about the vectors of cybersecurity.
MSBuild Malware IOCs:
Project File | Payload | C2 | Details |
---|---|---|---|
45c94900f312b2002c9c445bd8a59ae6 | Remcos 04fc0ca4062dd014d64dcb2fe8dbc966 | 135.181.170.169:50845 | |
d8a57534382a07cc0487b96350bca761 | Remcos eb8b1d64429e00f2b3b49f886ee3b0b4 | http://dl4.joxi.net/drive/2021/04/15/0048/3592/3153416/16/b8c104ce64.png | |
d52d6bad3d11e9a72998608ccca572f5 | Remcos 41c0bb6e89ad89af8eef7bec40d4acbb | ||
d66740b3ed3884c31d40e3747684411e | RedLine 302207c3248257d4d9badf4bc4b75483 | svhost-system-update.net:80 | http://dl4.joxi.net/drive/2021/04/19/0048/3592/3153416/16/d07409594a.proj |
43660f882cc5971ab83a810398487317 | RedLine 6d3e8a2802848d259a3baaaa78701b97 | 37.1.206.16:7575 | |
192b8ee95537dda7927ba3b45183e6a4 | Remcos b8e9ce084d9d49f565f850c59b003bcf | http://joxi.net/52ap4j7tkJER7m.proj | |
1ae425ac2890283ddcf11946e7e8f6ae | QuasarRat 723f5e75239b66e3d08b83a131c7b66c | ||
20621960888a6299123ce5a2df5eabba | Remcos f174c03d177a04e81677e9c9a9eae0c8 | ||
27b62f7b4b285b880b8c81960aa60b15 | Remcos cf45b793bc9ec86bfedfa165c01ede15 | ||
2d15a4c9184878e25bdf108bd58290b8 | Remcos de2ff99ca086a8ad0f9b8027aef696ba | ||
37bbbbc44c80ff4fe770ce78f6a37ebd | Remcos 73790d28f4f8f0f4c402da66c8dc393f | ||
603b1cc2d5488dcd8bb0a3b14429c88b | Remcos 23c5bc4a2e69c3f171561b524ceb4098 | ||
62c8efb35b3b9c10e965ec5a236fed2d | Remcos 4def35aedc86a946c13118e14127e0e9 | ||
a948e8d3222b9fa8ccbd091230098b78 | Remcos 85c700ff566161c77a03f282fa48a246 | ||
ecdb2860af9ce2754d178c80e3303080 | QuasarRat 7870a7c7e355d1fbf357c846d8bf2aea | ||
fe84ead033bfeaee70f84d8733b51e08 | RedLine 4023e57ffbc87aa93621a7c2a6f0b425 |
VirusTotal Detection Score:
Virus detection score
Security Vendor’s Analysis in vwnfmo.lnk
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Arun KL
Arun KL is a cybersecurity professional with 15+ years of experience in IT infrastructure, cloud security, vulnerability management, Penetration Testing, security operations, and incident response. He is adept at designing and implementing robust security solutions to safeguard systems and data. Arun holds multiple industry certifications including CCNA, CCNA Security, RHCE, CEH, and AWS Security.