10 Evil User Tricks for Bypassing Anti-Virus

Add Anti-Virus Policy Exceptions

A fun option that occasionally works is creating custom exceptions to the anti-virus solution’s policy. For example, an end user could create an exception that would allow all files with the “.exe” extension to run on the system. As a result, most malware and “hacker tools” would not get blocked or deleted.

This is less common in recent years, but historically non-administrative users had the privileges to disable many anti-virus solutions via the GUI interface. It used to be as simple as right-clicking the taskbar icon and choosing disable. As you can imagine, the skill level required to execute this bypass is low, but the risk to an organization is high.

Terminate Anti-Virus Processes

Some anti-virus solutions consist of multiple services that like to continuously restart each other. That’s when terminating the process before disabling a service can come in handy. Usually the taskkill command can be used. That’s essentially what the Metasploit post module “killav” does.

Stop and Disable Anti-Virus Services

In some cases users don’t have the privileges to disable anti-virus via the GUI, but they do have control over the associated services. If that is the case, then anti-virus services can usually be stopped and disabled. This can be accomplished via services.msc, the “sc” command, or the “net stop” command. However, always make sure to be a good little pentester and restore the services to their original state before logging out of the system. To stop a Windows service issue the following command:

net stop “service name

To disable a Windows service issue the following command:

sc config "service name" start= disabled

The services.msc console can be also be used to stop and disabled services via a GUI interface.  It can be accessed by navigating to start->run, and typing “services.msc”.

Disable Anti-Virus via Debugger Setting

This is a very cool trick that Khai Tran told me about. The original article he referenced can be found at http://blogs.msdn.com/b/greggm/archive/2005/02/21/377663.aspx. I recommend taking a look at it. In short, it says that users have the ability to prevent anti-virus from running by setting a custom debugger in the registry. When the operating system or user attempts to execute anti-virus the specified debugger is executed instead. Very clever, Internet, very clever. Apparently this has been used by malware developers for years. The basic steps for conducting the attack have been provided below. Please note that these were taken from the link above.

  1. Run regedit.exe
  2. Go to HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows NTCurrentVersionImage File Execution Options
  3. Create a new key (example: calc.exe)
  4. Create a new string value under your exe. The name of the string value is ‘Debugger’, and the value is svchost.exe (or anything)

Uninstall Anti-Virus Software

Although I don’t recommend uninstalling anti-virus during a penetration test, it can still be considered a valid bypass method. Some solutions may require a password before the uninstall process can begin. In those instances, the password can usually be found in the registry or an ini file on the system. However, other bypass methods are available like the one described within the article link below. It recommends simply terminating the “msiexec.exe” process when prompted for the uninstall password. http://helpdeskgeek.com/help-desk/uninstall-symantec-endpoint-protection-without-a-password/

Execute from a UNC Path or Removable Media

Some solutions are not configured to scan or prevent the execution of malicious binaries from SMB or WebDAV when accessed via the UNC path. It’s strange, but true. As a result, attackers can simply map an evil share containing backdoors, hacker tools etc., and execute malware to their hearts’ content. I guess some people are under the impression that malware can’t be stored on network drives. Similarly, some solutions are not configured to scan or prevent the execution of binaries from removable media such as an SD card, iPod, or USB drive. It’s pretty common to drop evil USB drives during onsite social engineering engagements, so this one scares me a little.

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