Net-Worm.Win32.Lovesan

Lovesan is an Internet Worm which exploits the DCOM RPC vulnerability in Microsoft Windows described in MS Security Bulletin MS03-026.

Lovesan is written in C using the LCC compiler. The worm is a Windows PE EXE file about 6KB (compressed via UPX – 11KB when decompressed).

Lovesan downloads and attempts to run a file named msblast.exe.

The text is as follows:

I just want to say LOVE YOU SAN!!

billy gates why do you make this possible? Stop making money and fix your software!!

Symptoms of Infection:

• MSBLAST.Exe in the Windows system32 folder.
• Error message: RPC service failure. This causes the system to reboot.

How the Worm Spreads

Lovesan registers itself in the autorun key when the system reboots and launches itself every time the computer reboots in the future:

HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun



windows auto update="msblast.exe"

The worm then scans IP addresses, attempting to connect to 20 random IP addresses and infect any vulnerable machines. Lovesan sleeps for 1.8 seconds and scans the next 20 IP addresses.

Lovesan scans IP addresses following one of the patterns below:

1. In 3 out of 5 cases Lovesan selects random base IP addresses (A.B.C.D) where D is equal to 0, while A, B and C are random numbers between 0 and 255.
2. In the remaining 2 out of 5 cases Lovesan scans the subnet and gets the local IP address of the infected machine, extracts values A and B from it and sets D to 0. Then the worm extracts the C value.

   If C is less than or equal to 20, then Lovesan does not modify C. Thus, if the local IP address is 207.46.14.1 the worm will scan IP addresses starting from 207.46.14.0

   If C is greater than 20, than Lovesan selects a random value between C and C-19. Thus, if the IP address of the infected machine is 207.46.134.191 the worm will scan IP addresses 207.46.{115-134}.0

The worm sends a buffer-overrun request to vulnerable machines via TCP port 135. The newly infected machine then initiates the command shell on TCP port 4444.

Lovesan runs the thread that opens the connection on port 4444 and waits for FTP ‘get’ request from the victim machine. The worm then forces the victim machine to sends the ‘FTP get’ request. Thus the victim machine downloads the worm from the infected machine and runs it. The victim machine is now also infected.

Other Information

Once a computer is infected the system sends an error message about RPC service failure and may reboot the machine.

As of August 16, 2003 Lovesan will launch DDoS attacks on the Windowsupdate.com server.