Last Wednesday, I had some down time so I decided to hunt around in System32 to see if I could find anything of potential interest. I located a few DLL files that shared an interesting export function called OpenURL: While looking for a quick win, I wanted to see if anything could be invoked without much effort. Sure enough, url.dll allowed for the execution an HTML application (.hta) using these commands: rundll32.exe url.dll,OpenURL "local\path\to\harmless.hta" rundll32.exe url.dll,OpenURLA "local\path\to\harmless.hta" After a few more functional tests across platforms, I (prematurely) posted this on Twitter, and the initial feedback was incredibly fast, educational, and humbling. On one hand, I should have went through a few more test routines to understand what was actually happening under the hood prior to posting. Conversely, it was incredible to see the instant reaction from some of the best practitioners in the field who helped triage this in what seemed like a matter of minutes. Big thanks to @subTee, @r0wdy_, and @Hexacorn for their rapid analysis! In short, the HTA was invoked using the OpenURL function, allowing for pass-thru command execution and lateral movement.