The Chinese threat actor known as APT17 and DeputyDog has been using profile pages and forum threads on Microsoft’s TechNet web portal to host IP addresses for command and control (C&C) servers.
Researchers at FireEye Threat Intelligence and the Microsoft Threat Intelligence Center have prepared a brief report on the advanced persistent threat (APT) actor’s C&C obfuscation techniques.
Experts have determined that the attackers haven’t actually compromised Microsoft’s website. Instead, they are using the portal’s legitimate functionality to host encoded strings that hide C&C IP addresses.
APT17 is a Chinese threat group that has been targeting United States government organizations, the military, law firms, defense contractors, IT firms, mining companies, and NGOs. One of the tools leveraged by the group is BLACKCOFFEE, a backdoor that can be used to upload and download files, create a reverse shell on the infected system, enumerate files and processes, manipulate files, and terminate processes.
The malware, which has been used by APT17 since at least 2013, now gets the IP address of the C&C server it’s supposed to communicate with from an encoded string embedded on the TechNet portal.
The new version of BLACKCOFFEE contains URLs that point to TechNet forum threads or biography sections in profiles created by the attacker. The encoded string that hides the IP address in plain sight is found in profiles and posts between the “@MICROSOFT” and “CORPORATION” tags.
In one example mentioned in the report from FireEye and Microsoft, the encoded IP address was published by the attackers in a forum post that appeared to contain useful information for solving a user’s problem.
Once the IP for the C&C is obtained, the malware starts communicating with the server. BLACKCOFFEE uses the C&C server to receive commands and to send information stolen from the infected device back to the malicious actors.
“If the C2 server is discovered or shut down, the threat actors can update the encoded IP address on TechNet to maintain control of the victims’ machines,” the companies explained in the report.
Experts have pointed out that the use of a legitimate service, dubbed by some a “dead drop resolver,” and the embedding of an encoded IP address benefits the attackers because it delays detection, and can prevent the discovery of the C&C server’s IP address. FireEye believes other threat groups are already using, or will use, variations of this technique in their operations.
“After discovering the BLACKCOFFEE activity, the FireEye-Microsoft team encoded a sinkhole IP address into the profile pages and forum threads and locked the accounts to prevent the threat actors from making any changes,” the report noted. “This collaborative approach allowed the team to observe the malware and its victims. With this information, Microsoft and FireEye can work with the anti-virus community to generate signatures to identify and clean systems affected by the malware and alert other forum and message board managers to be on the lookout for this technique.”