Grayfly: Chinese Threat Actor

Sidewalk was recently documented by ESET, who attributed it to a new group it called SparklingGoblin, which it linked to the Winnti malware family.
Symantec’s Threat Hunter Team has attributed Sidewalk to Grayfly, a longstanding Chinese espionage operation.
Members of the group were indicted in the U.S. in 2020.
The recent campaign involving Sidewalk suggests that Grayfly has been undeterred by the publicity surrounding the indictments.

Grayfly (aka GREF and Wicked Panda) is a targeted attack group that has been active since at least March 2017 using a custom backdoor known as Backdoor.Motnug (aka TOMMYGUN/CROSSWALK), a custom loader called Trojan.Chattak, Cobalt Strike (aka Trojan.Agentemis), and ancillary tools in its attacks.

Grayfly has been observed targeting a number of countries in Asia, Europe, and North America across a variety of industries, including food, financial, healthcare, hospitality, manufacturing, and telecommunications.
In more recent activity, Grayfly has continued with its focus on telecommunications but has also been observed targeting organizations operating within the media, finance, and IT service provider sectors.
Typically Grayfly targets publicly facing web servers to install web shells for initial intrusion, before spreading further within the network.

Once a network has been compromised, Grayfly may install its custom backdoors onto additional systems.
These tools allow the attackers to have comprehensive remote access to the network and proxy connections allowing them to access hard-to-reach segments of a target’s network.

Although sometimes labeled APT41, Grayfly is considered the espionage arm of APT41.
Similarly, Symantec tracks other sub-groups of APT41 separately, such as Blackfly, its cyber-crime arm.

A characteristic of the recent campaign was that the group appeared to be particularly interested in attacking exposed Microsoft Exchange or MySQL servers.
This suggests that the initial vector may be the exploit of multiple vulnerabilities against public-facing servers.

In at least one attack, the suspicious Exchange activity was followed by PowerShell commands used to install an unidentified web shell.
Following this, the malicious backdoor was executed.

After the installation of the backdoor, the attackers deployed a custom version of the credential-dumping tool Mimikatz.
This version of Mimikatz has been used previously in Grayfly attacks.