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PowerShell Virus

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#1 looselyrigorous


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Posted 12 August 2016 - 03:57 AM

Reposting from the "Am I infected" section after being directed here.



About 3 4 months ago we had an infection in our office. I wasn't there when it happened but from what I can tell someone plugged their usb stick in more than one(!!!) of the computers, and opened a bunch of files maybe. I could take a somewhat educated guess and say it was some MSOffice file with a macro in it but I could be wrong. The machines at that time had Windows 7 installed in them. I used MBAM/RogueKiller/HitmanPro to detect for viruses, came up with a bunch and cleaned them up. I sadly don't have any logs from that point of time since it seemed that everything was clean, after repeated scans with aforementioned utilities. Edit: I found a log from MBAM, which I am attaching here. I also did not install any other Antivirus solution, but upgraded to Windows 10 which came bundled with MSE.
Now 6 days ago I decided to install Avast on the most severely affected computer and did a scan which checked out clean. After some time generally using the computer (to see how avast impacted perf.) avast pushed a notification window saying it prevented some kind of malicious runtime. It was classified as "BV:AndroDrp [Drp]" or something along those lines. I can't say for certain because avast (in it's infinite wisdom) decided this wasn't worth logging. At all. The referenced executable (as you might imagine) was PowerShell.
So I kinda panicked there seeing as I had to look for a ghost. Then today comes and I managed to shed some light in the problem (or so it seems). An initial search didn't yield anything as far as PowerShell logs are concerned but then I came across this, which prompted me to doodle around in the Event Viewer Application Logs. Navigating to "Application and Services Logs > Microsoft > Windows > Powershell", I found a bunch of event's under ID 4104: "Execute a remote command". The events detailed the "ScriptBlocks" that were being ran. I took and reconstructed them. Mostly obfuscated variables and use of addition/concatenation to create another script and run it. Said script is some version of "Invoke-ReflectivePEInjection.ps1" from PowerSploit. It pulled the entire Script and the arguments it passed to it from Registry.
So far it doesn't seem like the "Virus" propagates through a local network. One of the Computers where the usb wasn't plugged in hasn't logged any PowerShell activity.
And that's the extent of what I've figured out so far. I don't know what it does after that but if someone wants to have a look you can ask. I'm more concerned with what is injected and what damage it may have caused, than cleaning it.  My trust in the current installations was somewhat shaken to begin with but now I'm probably going to reinstall Windows in one of them, try to clean the other one (the logs you're getting are from the installation I will try to clean).
Any and all help is greatly appreciated. Thank you!

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