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October 20, 2021Rewterz Threat Alert – FormBook Malware – Active IOCs
October 20, 2021
Severity
Medium
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
- 233a864f2f23497d4623337da7372e12
- 4d093da4d7c10d4b14a54f4793fee6ce
SHA-256
- 62f94256e7fc124c7292edefd8b589dad48601ff53d4058848b91a788a981e14
- 2d320ee3c680e6b5c2cbf5a781895dac33cf08190e3db8805dd9775ec4bd87d3
SHA-1
- 56eea34b0ab09a49daec844f08e2ea05747a37b5
- 1d726d4ed85efb342065713c40f968f660029fe8
Remediation
- Block all threat indicators at your respective controls.
- Search for IOCs in your environment.