Hackers are exploiting the self-extracting archives (SFX) feature of compression software like WinRAR or 7-Zip to plant backdoors without triggering security agents on the target system. Access to these files can be password-protected to prevent unauthorized access.
SFX files are used to simplify the distribution of archived data to users that do not have a utility to extract the package. Cybersecurity company CrowdStrike spotted the SFX abuse during a recent incident response investigation.
CrowdStrike’s analysis discovered an adversary that used stolen credentials to abuse ‘utilman.exe’ and set it to launch a password-protected SFX file that had been planted on the system previously. Utilman is an accessibility application that can be executed before user login, often abused by hackers to bypass system authentication. The SFX file triggered by utilman.exe is password-protected and contains an empty text file that serves as a decoy.
The real function of the SFX file is to abuse WinRAR’s setup options to run PowerShell, Windows command prompt (cmd.exe), and task manager with system privileges.
The attacker added multiple commands to run after the target extracted the archived text file. While there is no malware in the archive, the threat actor added commands under the setup menu for creating an SFX archive that would open a backdoor on the system.
WinRAR offers a set of advanced SFX options that allow adding a list of executables to run automatically before or after the process, as well as overwrite existing files in the destination folder if entries with the same name exist.
Crowdstrike claims that malicious SFX files are unlikely to be caught by traditional antivirus solutions. The researchers advise users to pay particular attention to SFX archives and use appropriate software to check the content of the archive and look for potential scripts or commands scheduled to run upon extraction.
In conclusion, hackers are increasingly using SFX files to plant backdoors without triggering security agents on the target system, making it difficult for traditional antivirus solutions to detect them.
Users are advised to use appropriate software to check the content of the archive and look for potential scripts or commands scheduled to run upon extraction.
