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

• Unauthorized Access
• Exposure of Sensitive Data

Indicators of Compromise

MD5

• b5a099246bec080e384b19fff56bb2cc
• cc59270baf11196c3414204c319f3be9

SHA-256

• 352fa41bf3319718aa0346e6feb3032c10241ca746ffd8acfe7cf5fe222be991
• 5c5890fdbc0c59e911168a0b618436e8fb76be6053ab0bfa2eec4f7f0e9267e6
• 24cf2b0fe84f6f53b85def931015f4a98c0af8a834f6dcc09581b7ad0ed74f8c
• ec2cc82773e2eaca5223bac427db22240d047139c3b0926df4d092612a3bf3f2
• 679c83aee6ed627ce5cb4641b798d461363ff103b8894c6f1808114018b5e7bc
• 25fc99f93932f10299fbe3b9ee2cad331f9d6ada033e6ade943b8d779f4dfe7d
• c168afed57a9b2960b58ff8a99afabcac9eaf4c341cf489f412d27d9a4494e54
• 741cd5c361878f530e5641891a34089375b53d7f52eebb98e7ed9195bb5b1a72

SHA-1

• 6f26990f3f471717c97dca80a2ccbf2eac952280
• 038e2aa526fad8eb762e21e9aed7eab4531d4e11

Remediation

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