Hackers Launching FlawedAmmyy Malware Via Undetected MS Excel Macros that Carried Powerful Backdoor

Threat actors from TA505 currently spreading powerful FlawedAmmyy RAT via weaponized MS Excel documents with malicious Excel 4.0 macro which is hard to detect by standard security controls.

Observed FlawedAmmyy RAT sample is highly sophisticated that can control the infected victims remotely and evade the security software.

TA505 threat actors are a well-known cybercrime group that has been already infected millions of victims using various malicious operations including large-scale Dridex, Locky, and GlobeImposter campaigns, among others.

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Based on the malware capabilities, it will be detected only when it passed the first level of execution by MSI file (Windows installer).

Researcher was dig deeper into leaked source analysis that reports, FlawedAmmyy RAT can perform various operation including remote desktop control, file system manager, proxy support and audio chat.

Apart from these infections it also can provide complete access of victim machines to the attackers and steal files, credentials, collect screenshots and access the camera and microphone. 

According to the Researcher, Pedro Tavares from seguranca–informatica said to “GBHackers On Security” via Email “During my research, I have detected a recent wave distributing the FlawedAmmyy RAT via XLM macros that complicate its detection via security endpoints such as AVs. I have submitted the sample onto the VirusTotal and no suspicious activity was detected. Thread Actor 505 (TA505) is now spreading this threat in order to infect user’s devices.”

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FlawedAmmyy Infection Process

TA505 Threat actors initially leveraging malspam email campaign to spreading the FlawedAmmyy RAT to the targeted victims using old tactics since the malware is not a new one.

The email contains attached Excel documents and the body content of the email trick users to open the file which carried and execute the malicious Excel 4.0 macro code.

“Malicious XLM macro code is located within a hidden form to avoid the attention of the victims. The name of the hidden form is written in the Russian language: Макрос1 — Macro 1, in English.”

After the successful execution of the Macro, MSI dropper will be ready drop the first stage of malware msiexec.exe process which is an another downloader of the original FlawedAmmyy  RAT ( wsus.exe ).

Later it establishes the C2 server communication where it receive the command from the attacker but the C2 server used by the attacker is now offline based on the researcher statement. you can also read the complete technical analysis details here.

“Users who receive emails with xls files attached should be aware as that files can be an undetected vehicle spreading any kind of malware and the Infection is dependent on the victim allowing the macro to run. Users should ensure that macros are disabled in their Microsoft Office applications. ” Researcher said.

Indicators of Compromise

Hashes
d490573977cc6b42ba0b4325df953a7f (.xls)
4cc5de3d2bddd7c89311fccf3d1b51d9 (.doc)
c4463d6ae741d4fb789bd0895fafebee (.msi installer/dropper)
2944eca03bc13b0edf064a619ec41459 (malware first stage)
4C4F2BBE3F49B17B04440C60F31293CB1431A867 (wsus.exe)
9B54BBB0730FD50789E13F1968043074EF30836C (wsus.exe)

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