Security vulnerabilities in remote desktop programs are being exploited by threat actors to deploy the PlugX malware, according to a new analysis by AhnLab Security Emergency Response Center (ASEC). The modular malware 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 in a September 2022 report. "This has been proven to be effective while infecting victims."