The TrickBot Trojan has switched to a new Windows 10 UAC bypass to execute itself with elevated privileges without showing a User Account Control prompt.

Windows uses a security mechanism called User Account Control (UAC) that will display a prompt every time a program is run with administrative privileges.

When these prompts are shown, they will ask logged in user if they wish to allow the program to makes changes, and if the program is suspicious or unrecognized, allows the user to prevent the program from running.

These UAC bypasses are found in legitimate Microsoft Windows programs that are used by the operating system to launch other programs. As they are not considered a high priority to Microsoft, it could be a while before discovered bypasses are fixed, if at all.

To avoid being detected, malware developers sometimes use a UAC bypass so that the malware runs with administrative privileges, but without displaying a UAC prompt and alerting the user.

Trickbot switches to the Wsreset.exe UAC bypass

trick bot

TrickBot

Just recently we found that TrickBot had begun using a Windows 10 UAC bypass that utilizes the legitimate Microsoft fodhelper.exe program. This week, ReaQta discovered that TrickBot has now switched to a different UAC bypass that utilizes the Wsreset.exe program. Wsreset.exe is a legitimate Windows program used to reset the Windows Store cache.When executed, Wsreset.exe will read a command from the default value of the HKCU\Software\Classes\AppX82a6gwre4fdg3bt635tn5ctqjf8msdd2\Shell\open\command key and execute it.

When executing the command it will not display a UAC prompt and users will have no idea that a program has been executed.This allows the trojan to run silently in the background while it harvests saved login credentials, SSH keys, browser history, cookies, and more. TrickBot is now exploiting this UAC bypass to launch itself with elevated privileges, but without the logged in Windows user being notified by a UAC prompt. TrickBot is particularly dangerous as it can propagate throughout the network and if it gains admin access to a domain controller, it can steal the Active Directory database to gain further credentials on the network. Eventually, TrickBot is known to open a reverse shell back to the Ryuk Ransomware actors so that they can encrypt the entire compromised network.