Hackers Exploiting Remote Desktop Software Flaws to Deploy PlugX Malware

Mar 09, 2023Ravie LakshmananThreat Intelligence / Malware

Security vulnerabilities in remote desktop programs such as
Sunlogin and AweSun are being exploited by threat actors to deploy
the PlugX malware.

AhnLab Security Emergency Response Center (ASEC), in a new analysis^[1], said it marks the
continued abuse of the flaws to deliver a variety of payloads on
compromised systems.

This includes^[2]
the Sliver post-exploitation framework, XMRig cryptocurrency miner,
Gh0st RAT, and Paradise ransomware. PlugX is the latest addition to
this list.

The modular malware^[3]
has been extensively put to use by threat actors based in China,
with new features continuously added to help perform system control
and information theft.

In the attacks observed by ASEC, successful exploitation of the
flaws is followed by the execution of a PowerShell command that
retrieves an executable and a DLL file from a remote server.

This executable is a legitimate HTTP Server Service from
cybersecurity company ESET, which is used to load the DLL file by
means of a technique called DLL side-loading and ultimately run the
PlugX payload in memory.

“PlugX operators use a high variety of trusted binaries which
are vulnerable to DLL Side-Loading, including numerous anti-virus
executables,” Security Joes noted^[4]
in a September 2022 report. “This has been proven to be effective
while infecting victims.”

The backdoor is also notable for its ability to start arbitrary
services, download and execute files from an external source, and
drop plugins that can harvest data and propagate using Remote
Desktop Protocol (RDP).

“New features are being added to [PlugX] even to this day as it
continues to see steady use in attacks,” ASEC said. “When the
backdoor, PlugX, is installed, threat actors can gain control over
the infected system without the knowledge of the user.”