Krei is a backdoor that provides access to the compromised computer for remote attackers. Krei affects Windows 2000 and XP systems only.
After removing these and restarting the system the backdoor and the kernel module can be deleted from the system.
Starting the computer in Safe Mode:
- 1, Restart the computer
- 2, Press F8 when the Windows loading screen appears
- 3, Choose Safe Mode from the menu
When first run it installs itself as a service using Service Control Manager. This makes sure that the backdoor will be run when the computer is started.
When Krei is active it listens on TCP port 961 waiting for the remote client to connect.
After Krei had been installed on the system the following key appears in the Registry:
The Krei trojan makes use of an external component that helps to hide it from all the conventional tools. This kernel component resides in a file called 'ierk8243.sys'. When this driver is loaded it creates a special device that can be used to control the hiding feature. This module hooks several low-level Windows API functions to make sure that the hidden processes, registry keys are not visible when this driver is active.
Since the kernel module hides both itself and the backdoor the removal requires the computer to be started in Safe Mode. In Safe Mode the following Registry keys have to be removed:
Description Created: F-Secure Corp, February 3rd, 2003
Technical Details: Gergely Erdelyi