TA505 APT Hackers Drop ServHelper and FlawedAmmyy through ISO files to Gain Remote Access

TA505 hacker group continues to evolve by making small changes with their techniques, target countries and combination of techniques for each their campaigns.

The group’s active campaigns found in April, June & July, in all the campaigns they continue to use FlawedAmmyy RAT or ServHelper variants as payloads.

According to TrendMicro report the group now targeting new countries such as Turkey, Serbia, Romania, Korea, Canada, the Czech Republic, and Hungary.

TA505 Entry methods

The new campaign targets banks in Turkish and Serbian contains an .ISO file as an attachment, this method is not new with TA505 hacker group.

They use the following methods as an entry point,

• ISO image attachments
• .NET downloader
• New style for macro delivery
• Newer version of ServHelper
• .DLL variant of FlawedAmmyy downloader

The attack starts with an Email that includes ISO image is an .LNK which then uses a msiexec Windows installer to install the file downloaded from hxxp://139[.]180[.]195[.]36/pm2.

The pm2 file includes another executable that created through Nullsoft Scriptable Install System for Microsoft Windows that installs ServHelper.

Researchers found multiple samples, in another sample they found an Excel attachment with malicious macros, another sample has an updated version of ServHelper and another sample with an execution error.

They also made changes with C&C communication, previously it was unencrypted, now they use XOR encoding/URL encoding.

The group continues to use ServHelper and FlawedAmmy RAT and includes document embedded with malicious commands and strings.

“A campaign targeting China spoofed FedEx-themed emails with subjects about delivery problems, failures, or notifications. Instead of attachments, it had malicious URLs in the message content that lead to the download of a malicious document.”

“The changes and adjustments that TA505 made from the original ServHelper and FlawedAmmyy routines may indicate that the group is experimenting and testing to determine which forms of obfuscation can bypass detections, resulting in more financial returns.”

The group continues to target different business sectors and they continue to use phishing and social engineering techniques to compromise systems.

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