Rewterz Threat Alert – ServHelper Backdoor – Active IOCs

Severity

High

Analysis Summary

ServHelper that is associated with the hacking group TA505 has been seen targeting financial and retail sectors. With the help of this backdoor, it enabled them to install and deploy other malware like Information Stealers (Predator Stealer), and Remote Access Trojans (RAT) (FlawedAmmy, NetSupport). It is delivered via NSIS installer, which, typically arrives as an attachment to a lure-based email. The loader checks to see if it is running in a virtualized environment to evade analysis techniques. It does this by checking for the presence of a Windows Defender file known to be present in virtualized environments. If this file is present, the installation will stop. If the file is not present, the installation proceeds. A PowerShell script contained within the NSIS installer’s directory is then executed. This script decrypts and invokes the main installer of ServHelper. Encryption is done with a combination of Base64 encoding and Triple DES Algorithm. This prevents commands from appearing in plain text. A further set of verification checks are done. The installer checks to ascertain if the instance has administrator privileges. If not, the installer will attempt to escalate privilege using DLL hacking with the assistance of Fubuki from UACME. This readily available collection of tools is typically used by penetration testers for research and privilege escalation. The installer also checks to see if the ROM size is greater than 2MB. If there is no ROM file, the installation stops as this is an indicator of virtualization. Once all components are decrypted, dropped, and installed, the ServHelper DLL is loaded. This specific variant only targets 64-bit Windows Operating Systems. Once the installation is complete, threat actors have backdoor access and are able to send and receive information.

Impact

• File Encryption
• Exposure of Sensitive Data
• Information Theft
• Cryptomining

Indicators of Compromise

MD5

• b7df367405df1d63dd0b77952f864d39
• 5cfa3b3e19ba458fc1459abd524532fd

SHA-256

57214113a306cb06d2f41b4092c0c0ad3945ee7f5a8cc9381cfb4ba9ac2d8fc6
b5e776f84f8f01fcc1fb822ff5612afe62097bf367ced2187fda0b5bf3d652ee

SHA-1

• 0a4ead8259be4064ee7403833749bcb5a7464d72
• 24b8d9f57c1a10b58b6962dcfc21405a6fd0b756

Remediation

• Block all the threat indicators in your respective controls.
• Search for IOCs in your environment.