AuKill – A Malware That Kills EDR Clients To Attack Windows Systems

A new hacking tool, AuKill, disables Endpoint Detection & Response (EDR) software for threat actors to launch BYOD attacks by deploying backdoors and ransomware on targeted systems.

Sophos researchers witnessed the usage of AuKill in two incidents where an adversary first deployed Medusa Locker ransomware and another instance where the attacker installed LockBit ransomware after using the EDR killer on an already compromised system.

While the threat actors use validly signed drivers with kernel privileges to disable security solutions and seize control of victims’ devices in these attacks.

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Technical Analysis

AuKill malware deploys a malicious variant of Windows driver (procexp[.]sys) next to Microsoft’s Process Explorer v16.32, a widely-used tool for gathering data on active Windows processes.

To gain privileges, it verifies if it is already operating with SYSTEM privileges. If not, it emulates the TrustedInstaller Windows Modules Installer service to elevate to the SYSTEM level.

AuKill starts multiple threads to repeatedly scan and terminate security processes and services to deactivate security software.

AuKill relies on a Process Explorer driver on compromised devices and systems to disable security solutions like Backstab.

So, they both have many similarities; the only difference is that AuKill is not an open-source tool, unlike Backstab.

Sophos X-Ops identified the LockBit gang using Backstab in at least one attack during their investigation of LockBit 3.0 (LockBit Black).

The malware uses a simple arithmetic calculation to validate the password or key.

It calculates the decimal value of each character’s ASCII code, doubles it, adds it to the next character’s value, and repeats the process.

Moreover, to disable EDR components, the following functions are used:-

• Terminate Via Procexp
• Terminate Forcefully
• Disable Services
• Unload Drivers

AuKill Timeline

Since the start of 2023, the tool has been used in three ransomware incidents to disable target protection and execute the ransomware.

After using the tool, attackers deployed the Medusa Locker ransomware in January and February. Similarly, in February, an attacker deployed Lockbit ransomware immediately after using AuKill.

Sophos researchers gathered six distinct versions and monitored their functional alterations over three months. 

For easy identification, cybersecurity researchers at Sophos have labeled the earliest iteration of the malware as AuKill V1, while the latest version is AuKill V6.

They have a function that regularly inspects EDR processes and services to prevent revived processes from running.

Recommendations

Here below we have mentioned all the recommendations below:-

• Make sure your endpoint security product has tamper protection implemented.
• Ensure that your Windows security roles are correctly configured.
• Make sure your system is always up-to-date.
• Besides your OS, regularly verify for updates to your computer’s applications and tools.
• Consider removing outdated tools that are no longer necessary or used.
• Having a vulnerable driver on the system may also allow legitimate driver abuse.
• Ensure an effective vulnerability management program to prevent legitimate driver abuse.

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