A new wave of Zhelatin emails is currently going out. A typical example is this email:
Greetings, Are you ready to have fun at Web Joker. Account Number: 775152935455 Temp Login ID: user1160 Your Password ID: px259 Please keep your account secure by logging in and changing your login info. Use this link to change your Login info: http://74.64.28.xx/ Enjoy, Confirmation Dept. Web Joker
The page linked to in the email advises the user to install a “Secure Login Applet” to view the page, which of course is an executable trojan file — a typical name is applet.exe. Below is a brief analysis.
The applet.exe file, when run, performs the standard Zhelatin actions: Copying itself to C:\Windows\spooldr.exe, and extracting a driver file to C:\Windows\system32\spooldr.sys. It also adds a rename entry for a .tmp file:
HKLM\System\CurrentControlSet\Control\Session Manager\PendingFileRenameOperations = C:\Windows\system32\drivers\OLD3.tmp"
This entry will simply delete the file on reboot. Interestingly enough, the variants we’ve examined so far haven’t patched the tcpip.sys file to make themselves autostart. This makes removal easier since tcpip.sys does not need to be restored from backup. (Check that the digital signature on tcpip.sys is valid though, in case you are infected with this and it is a different variant!)
The OLD3.tmp file is actually a patched version of the legitimate Microsoft kbdclass.sys driver file. The trojan version has an extra 15 KB of data appended to it. The entry point of the patched driver file has been modified to point to the start of this extra block of data. Once loaded, the OLD3.tmp file loads the spooldr.sys trojan driver using the native Windows API function ZWSetSystemInformation.
The spooldr.sys driver will as usual disable most common firewalls, including the built-in Windows firewall.
Manual removal steps
- Reboot computer in Safe Mode without networking
- Delete the following files: C:\Windows\spooldr.exe, C:\Windows\system32\spooldr.sys
- Restart computer normally