Cobalt Strike Malware (W32/Cobalt) – What is It and How to Remove It

This article aims to explain what is Cobalt Strike malware, how does it infect computers and how to remove it effectively from your computer.

New form of malware has been reported to cause infections via a vulnerability for Windows Machines that is 17 years old. The virus, related to the pen-testing (penetration testing) tool Cobalt Strike is also dubbed Cobalt Strike malware and it’s primary goal after infecting your computer is to turn it into a slave of the hackers who are behind the infection. In the event that you have seen W32/Cobalt or other similar detection on your computer, we recommend that you read this article and learn how to fully remove the Cobalt Strike malware from your PC and protect it against future infections and intrusions.

Threat Summary

Name	Cobalt Strike Malware
Type	JavaScript Malware Infection
Short Description	Aims to make your computer remotely controlled via shell commands by the hackers behind the virus.
Symptoms	No symptoms so far as the malware is file-less, but your computer may behave strange and can contain other malware in it.
Distribution Method	Via malicious URLs or compromised websites.
Detection Tool	See If Your System Has Been Affected by Cobalt Strike Malware Download Malware Removal Tool
User Experience	Join Our Forum to Discuss Cobalt Strike Malware.

Cobalt Strike Malware – Infection Analysis

In order to cause a successful infection, the malicious file of this virus is actually a semi-legitimate Microsoft Word document, which pretends to be a legitimate file sent by a bank or a big company. The file itself infects via malicious macros which contain the exploit CVE-2017-11882 that is over 17 years old at the time of writing this. So far, what is known about this vulnerability is that it was only patched once, two weeks after it was discovered by Microsoft.

The way the cyber-criminals who are believed to be the Cobalt hacker group have decided to use malicious macro infections for their attacks in e-mails that they pretend are from Visa. One sample was detected by malware researchers Jasper Manual and Joie Salvio at Fortinet and it uses the following e-mail:

The message (In Russian) pretends to come from Visa’s payWave system and it aims to get the victim to open what appears to be a .zip and .doc files that pose as “New security system changes in Visa payWave”. Once this document is opened, the victim sees a legitimate Microsoft Word file that only says the words “Enable Editing”:

In reality however, the file triggers a script for PowerShell which initiates the download of the infection file of Cobalt Strike, while obfuscating it with the CVE-2017-11882 vulnerability. The whole process of initiating the download is done by taking control of the Microsoft HTML Application Host also known as the process mshta.exe, that has a purpose to execute HTML apps. The result of this is that the mshta.exe service connects to the IP address 104.254.99.77 and downloads the JavaScript infection payload of Cobalt Strike on the victim’s computer. But what is downloaded is not the final JavaScript payload, but instead this JavaScript triggers another download from the host 104.254.99.77 which downloads a file with a random name and the .ps1 suffix on the victim’s computer. The file is located in the %AppData% directory and may appear like the following:

→ %AppData%\28dh32d9233.ps1

When this .ps1 file is executed, the actual Cobalt Strike infection takes place on the victim’s computer.

Cobalt Strike Malware – Malicious Activity

Once downloaded, the .ps1 file, belonging to Cobalt Strike is automatically activated. It triggers yet another PowerShell script which has the client DLL files of Cobalt Strike – a rather outdated, but still very effective tool, previously used for penetration testing of the defenses in Windows Operating Systems. Once it detects whether your Windows is running based on 32-bit or 63-bit architecture, the appropriate Cobalt Strike DLL is executed directly in your Windows PowerShell memory and this results in the malware not being actually present on your drive, while remaining embedded in PowerShell and even if you delete the .ps1 file, the virus is still active on your PC. This also helps any antivirus programs that are conventional to detect the virus.

Once the DLL of Cobalt Strike is triggered, the cyber-criminals have obtained complete control of your computer system – it belongs to them. They can perform all of the activities which can be performed using the Cobalt Strike shell commands themselves. Here is only a small part of commands that may be triggered, using Cobalt malware:

→ spawnto – spawns sessions into processes.
inject – injects various malicious scripts in legitimate Windows processes.
dllinject – same as inject but for DLLs
download – can download other malware or files on your computer.
upload – can upload files to the hacker’s server, i.e. it can steal your files.
timestomp – to assist with blending files, obfuscation and updating itself.
ls – similar to Linux, it helps you to list different files.
mkdir – to create folders on your computer.
keylogger pid – to log your keystrokes.
screenshot pid – to take a screenshot of your desktop.
jobkill – to kill a job.
socks 8080 – to set a Proxy server on a selected port (in this case 8080).

These are only the main commands that are likely to be used on your computer and you have no way of knowing that they are triggered as it all happens in the background of your computer. The full list of commands can be seen on Cobalt Strike’s web page.

How to Remove Cobalt Strike Malware from Your PC

In order to remove this malware, you will need to have some experience in Working with Windows PowerShell and definitely some malware removal experience. So if manual removal is not your type of thing to do, security experts strongly recommend to use an advanced malware removal tool instead of conventional antivirus program. Such software will not only automatically scan for and remove Cobalt Strike malware from your computer, but will also make sure that your computer stays protected against other JavaScript and PowerShell infections in the future.

Manually delete Cobalt Strike Malware from your computer

Note! Substantial notification about the Cobalt Strike Malware threat: Manual removal of Cobalt Strike Malware requires interference with system files and registries. Thus, it can cause damage to your PC. Even if your computer skills are not at a professional level, don’t worry. You can do the removal yourself just in 5 minutes, using a malware removal tool.

1. Boot Your PC In Safe Mode to isolate and remove Cobalt Strike Malware files and objects

Boot Your PC Into Safe Mode

1. For Windows 7,XP and Vista. 2. For Windows 8, 8.1 and 10. Fix registry entries created by Cobalt Strike Malware on your PC.

For Windows XP, Vista, 7 systems:

1. Remove all CDs and DVDs, and then Restart your PC from the “Start” menu.
2. Select one of the two options provided below:

– For PCs with a single operating system: Press “F8” repeatedly after the first boot screen shows up during the restart of your computer. In case the Windows logo appears on the screen, you have to repeat the same task again.

– For PCs with multiple operating systems: Тhe arrow keys will help you select the operating system you prefer to start in Safe Mode. Press “F8” just as described for a single operating system.

3. As the “Advanced Boot Options” screen appears, select the Safe Mode option you want using the arrow keys. As you make your selection, press “Enter“.

4. Log on to your computer using your administrator account

While your computer is in Safe Mode, the words “Safe Mode” will appear in all four corners of your screen.

Step 1: Open the Start Menu

Step 2: Whilst holding down Shift button, click on Power and then click on Restart.
Step 3: After reboot, the aftermentioned menu will appear. From there you should choose Troubleshoot.

Step 4: You will see the Troubleshoot menu. From this menu you can choose Advanced Options.

Step 5: After the Advanced Options menu appears, click on Startup Settings.

Step 6: Click on Restart.

Step 7: A menu will appear upon reboot. You should choose Safe Mode by pressing its corresponding number and the machine will restart.

Some malicious scripts may modify the registry entries of your computer to change different settings. This is why manual clean up of your Windows Registry Database is strongly recommended. Since the tutorial on how to do this is a bit lenghty, we recommend following our instructive article about fixing registry entries.

2. Find malicious files created by Cobalt Strike Malware on your PC

Find malicious files created by Cobalt Strike Malware

1. For Windows 8, 8.1 and 10. 2. For Windows 7,XP and Vista.

For Newer Windows Operating Systems

Step 1:

On your keyboard press  + R and write explorer.exe in the Run text box and then click on the Ok button.

Step 2:

Click on your PC from the quick access bar. This is usually an icon with a monitor and its name is either “My Computer”, “My PC” or “This PC” or whatever you have named it.

Step 3:

Navigate to the search box in the top-right of your PC’s screen and type “fileextension:” and after which type the file extension. If you are looking for malicious executables, an example may be “fileextension:exe”. After doing that, leave a space and type the file name you believe the malware has created. Here is how it may appear if your file has been found:

N.B. We recommend to wait for the green loading bar in the navination box to fill up in case the PC is looking for the file and hasn’t found it yet.

For Older Windows Operating Systems

In older Windows OS’s the conventional approach should be the effective one:

Step 1:

Click on the Start Menu icon (usually on your bottom-left) and then choose the Search preference.

Step 2:

After the search window appears, choose More Advanced Options from the search assistant box. Another way is by clicking on All Files and Folders.

Step 3:

After that type the name of the file you are looking for and click on the Search button. This might take some time after which results will appear. If you have found the malicious file, you may copy or open its location by right-clicking on it.

Now you should be able to discover any file on Windows as long as it is on your hard drive and is not concealed via special software.

Automatically remove Cobalt Strike Malware by downloading an advanced anti-malware program

1. Remove Cobalt Strike Malware with SpyHunter Anti-Malware Tool

Remove Cobalt Strike Malware with SpyHunter Anti-Malware Tool

1. Install SpyHunter to scan for and remove Cobalt Strike Malware.2. Scan with SpyHunter to Detect and Remove Cobalt Strike Malware.

Step 1:Click on the “Download” button to proceed to SpyHunter’s download page.

Download

Malware Removal Tool

It is highly recommended to run a scan before purchasing the full version of the software to make sure that the current version of the malware can be detected by SpyHunter.

Step 2: Guide yourself by the download instructions provided for each browser.
Step 3: After you have installed SpyHunter, wait for it to automatically update.

Step1: After the update process has finished, click on the ‘Scan Computer Now’ button.

Step2: After SpyHunter has finished scanning your PC for any Cobalt Strike Malware files, click on the ‘Fix Threats’ button to remove them automatically and permanently.

Step3: Once the intrusions on your PC have been removed, it is highly recommended to restart it.

Optional: Using Alternative Anti-Malware Tools

Remove Cobalt Strike Malware Using Other Alternative Tools

STOPZilla Anti Malware

1. Download and Install STOPZilla Anti-malware to Scan for And Remove Cobalt Strike Malware.
Step 1: Download STOPZilla by clicking here.
Step 2: A pop-up window will appear. Click on the ‘Save File’ button. If it does not, click on the Download button and save it afterwards.

Step 3: After you have downloaded the setup, simply open it.
Step 4: The installer should appear. Click on the ‘Next’ button.

Step 5: Check the ‘I accept the agreement’ check circle if not checked if you accept it and click the ‘Next’ button once again.

Step 6: Review and click on the ‘Install’ button.

Step 7: After the installation process has completed click on the ‘Finish’ button.

2. Scan your PC with STOPZilla Anti Malware to remove all Cobalt Strike Malware associated files completely.
Step 1: Launch STOPZilla if you haven’t launched it after install.
Step 2: Wait for the software to automatically scan and then click on the ‘Repair Now’ button. If it does not scan automatically, click on the ‘Scan Now’ button.

Step 3: After the removal of all threats and associated objects, you should Restart your PC.

Vencislav Krustev

A network administrator and malware researcher at SensorsTechForum with passion for discovery of new shifts and innovations in cyber security. Strong believer in basic education of every user towards online safety.

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