The Cyber Security Review | Friday, November 04, 2022
Cranefly hackers are using Microsoft IIS logs to deliver malware, researchers warn. The aim appears to be intelligence gathering rather than ransomware or data theft.
FREMONT, CA:From ostensibly secure Internet Information Services (IIS) logs, Symantec researchers have discovered a new dropper (Trojan variant) that criminals use to distribute harmful software. The Trojan is allegedly being used by a threat actor known as Cranefly. Installing a fresh Trojan with a geppei dropper. Malicious software, including Danfuan malware.
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Cranefly was initially discovered by Mandiant when the company reported the activities of a group it designated UNC3524. According to the report, the crew made a considerable effort to target those involved in corporate development, mergers and acquisitions, and other major commercial operations. The attackers stayed on the target networks for at least 18 months while installing backdoors on unprotected devices. The attackers were viewed as downloading the QuietExit backdoor based on the open-source and free Dropbear SSH client-server application.
According to Symantec's latest caution, its researchers have found the Geppei dropper on numerous victim computers. When executing assaults using PyInstaller, Geppei can turn a Python script into an executable file. It interprets instructions from a formal IIS log, which monitors data from IIS, including web pages and applications. Attackers can deliver orders to a hacked web server by disguising them as requests for web access.
Although IIS logs the commands, as usual, Geppei can recognise them as instructions. Ashx files that Geppei reads contain maliciously encoded instructions. The location of the files' storage location, which serves as a backdoor, is determined by a command parameter. Threat actors frequently use the strings Wrde, Exco, and CIIo in the malicious HTTP requests that Geppei examines. None of these strings will typically be visible in the IIS log files. These strings appear to act as a catalyst for the dropper to operate.
Cranefly can deliver instructions using a URL that is either a dummy or doesn't exist because IIS records 404 errors in the same log file by default. One of the backdoors that Geppei drops is ReGeorg, a well-known web shell that Symantec and Mandiant have observed Cranefly using. ReGeorg is publicly available on GitHub and has previously been utilised by several advanced persistent threat (APT) groups.
Symantec claimed that despite the threat actor's prolonged stay on infected networks, in this case, 18 months, it has not detected any data exfiltration from victim workstations. The researchers came to the conclusion that Cranefly is a fairly skilled threat actor, given the deployment of a unique approach and proprietary tools, as well as the steps taken to mask evidence of this activity on victim workstations.
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