Botnet That Hid For 18 Months

An anonymous reader quotes a report from Ars Techinca: It's not the kind of security discovery that happens often. A previously unknown hacker group used a novel backdoor, top-notch tradecraft, and software engineering to create an espionage botnet that was largely invisible in many victim networks. The group, which security firm Mandiant is calling UNC3524, has spent the past 18 months burrowing into victims' networks with unusual stealth. In cases where the group is ejected, it wastes no time reinfecting the victim environment and picking up where things left off. There are many keys to its stealth, including: - The use of a unique backdoor Mandiant calls Quietexit, which runs on load balancers, wireless access point controllers, and other types of IoT devices that don't support antivirus or endpoint detection. This makes detection through traditional means difficult. - Customized versions of the backdoor that use file names and creation dates that are similar to legitimate files used on a specific infected device. - A live-off-the-land approach that favors common Windows programming interfaces and tools over custom code with the goal of leaving as light a footprint as possible. - An unusual way a second-stage backdoor connects to attacker-controlled infrastructure by, in essence, acting as a TLS-encrypted server that proxies data through the SOCKS protocol. The SOCKS tunnel allowed the hackers to effectively connect their control servers to a victim's network where they could then execute tools without leaving traces on any of the victims' computers. A secondary backdoor provided an alternate means of access to infected networks. It was based on a version of the legitimate reGeorg webshell that had been heavily obfuscated to make detection harder. The threat actor used it in the event the primary backdoor stopped working. [...] One of the ways the hackers maintain a low profile is by favoring standard Windows protocols over malware to move laterally. To move to systems of interest, UNC3524 used a customized version of WMIEXEC, a tool that uses Windows Management Instrumentation to establish a shell on the remote system. Eventually, Quietexit executes its final objective: accessing email accounts of executives and IT personnel in hopes of obtaining documents related to things like corporate development, mergers and acquisitions, and large financial transactions. "Unpacking this threat group is difficult," says Ars' Dan Goodin. "From outward appearances, their focus on corporate transactions suggests a financial interest. But UNC3524's high-caliber tradecraft, proficiency with sophisticated IoT botnets, and ability to remain undetected for so long suggests something more."

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