Zebrocy APT Group Expands Malware Arsenal with New Backdoor Family

Zebrocy, a Russian-speaking advanced persistent threat (APT) actor associated with numerous attacks on government, military, and foreign affairs-related targets since at least 2015 is back at it again.

Researchers from Kaspersky Lab say they have observed the group using a new downloader to deploy a recently developed backdoor family on organizations in multiple countries, including Germany, the United Kingdom, Iran, Ukraine, and Afghanistan.

The backdoor, written in the Nim programming language, is designed to profile systems, steal credentials, and help the attackers maintain persistence on a compromised computer over an extended period of time. As with its previous campaigns, Zebrocy is using spear-phising emails to distribute the new malware to targeted organizations.

It is the latest addition to Zebrocy's continually expanding malware set and demonstrates the group's long-term commitment to gaining access to targeted networks, Kaspersky Lab said in a report Monday. "We will see more from Zebrocy into 2019 on government and military related organizations," the security vendor noted.

Zebrocy and its eponymously named malware first surfaced in 2015. Kaspersky Lab and other security vendors have linked Zebrocy to Fancy Bear/APT 28/Sofacy, a Russian-speaking APT group associated with attacks on numerous organizations including — most notoriously — the US Democratic National Committee in the run-up to the last general elections.

Some security firms, such as ESET, for instance, have described Zebrocy as Fancy Bear's attack toolset, and not necessarily as a separate group. Earlier this month ESET published a new report noting numerous improvements to the toolset to give attackers better control over compromised systems.

Kaspersky Lab itself considers the team using Zebrocy as a sort of separate subgroup that shares its lineage with Sofacy/Fancy Bear and the BlackEnergy/Sandworm APT group that is believed to be behind a series of disruptive attacks on Ukraine's power grid in 2015.

"For our part, we have referred to Zebrocy as a subset of Sofacy for the past several years," says Kurt Baumgartner, principal security researcher with Kaspersky Lab's Global Research and Analysis Team. Initially, at least, the group behind Zebrocy shared limited infrastructure, targeting, and code with Fancy Bear and the BlackEnergy group. "However, research over time shows that this malware set, activity, and infrastructure is unique," he says.

What makes Zebrocy somewhat different from other APTs is its tendency to build malware using a wide set of programming languages and technologies, including AutoIT, Delphi, C#, Go, PowerShell, and most recently Nim, Baumgartner notes.

Despite its links to two extremely sophisticated threat groups, Zebrocy has so far not exploited any zero-day security vulnerabilities in its campaigns. It also has shown a tendency to build its malware by copying and pasting legitimate and malicious code from sites such as Pastebin and GitHub. Often Zebrocy has recoded its malware for specific campaigns using bits and pieces of code obtained from external sources.

"It's very unusual to observe an APT with lineage in two groups known for zero-day exploit use and highly agile technical capabilities experiment and recode their malware in so many languages," Baumgartner says.

That fact and Zebrocy's tendency to rip source code from public forums and code-sharing sites suggest the group's sophistication lies in experimentation, and that the selection of the group's malware implementations are partially guided by machine learning algorithms, he notes.

"Network defenders already have a complicated enough time mitigating and clustering all the varieties of attacks thrown at them," Baumgartner says. "Zebrocy’s constant experimenting and changing malware only compounds those problems."