A new variant of the Welchi RPC worm was found on February 12th, 2004.
This variant is functionally quite similar to the original virus.
It copies itself on the infected system as SVCHOST.EXE.
The worm contains links to several security patches and will try
to install them. Welchi.B will also try to remove Mydoom.
It might display a text saying "LET HISTORY TELL FUTURE !" and references
to the dropping of atomic bombs during seconds world war.
The worm will start by creating a mutex named "WksPatch_Mutex" after which it
will install itself as a service.
It copies itself to the Windows' System folder as "svchost.exe"
Whenever the system's date is within the month of June it will remove itself.
On certain occasions the worm attempts to download one of the following Windows
patches:
http://download.microsoft.com/download/4/d/3/4d375d48-04c7-411f-959b-3467c5ef1e9a/WindowsXP-KB828035-x86-CHS.exe
http://download.microsoft.com/download/a/4/3/a43ea017-9abd-4d28-a736-2c17dd4d7e59/WindowsXP-KB828035-x86-KOR.exe
http://download.microsoft.com/download/e/a/e/eaea4109-0870-4dd3-88e0-a34035dc181a/WindowsXP-KB828035-x86-ENU.exe
http://download.microsoft.com/download/9/c/5/9c579720-63e9-478a-bdcb-70087ccad56c/Windows2000-KB828749-x86-CHS.exe
http://download.microsoft.com/download/0/8/4/084be8b7-e000-4847-979c-c26de0929513/Windows2000-KB828749-x86-KOR.exe
http://download.microsoft.com/download/3/c/6/3c6d56ff-ff8e-4322-84cb-3bf9a915e6d9/Windows2000-KB828749-x86-ENU.exe
It will scan the computer for files with extensions from the following list:
.shtml
.shtm
.stm
.cgi
.php
.html
.htm
.asp
And overwrite them with and HTML contained within the worm's body, the exact
HTML code follows:
<html>
<body text="#FF0000" bgcolor="#000000"
<font size="7" face="Arial">
<p align="center">
LET HISTORY TELL FUTURE !<br>
<br>
1931.9.18<br>
1937.7.7<br>
1937.12.13 300,000 !<br>
<br>
1941.12.7<br>
1945.8.6 Little boy<br>
1945.8.9 Fatso<br>
<br>
1945.8.15<br>
Let history tell future !<br>
</p>
</font>
</body>
</html>
Access to the Internet will be checked by attempting to resolve randomly any of:
microsoft.com
intel.com
google.com
In case of failure, it will wait for 20 minutes before attempting the operation
again.
Spreading.
The worm will spread through the backdoor left in the system by the Mydoom.A
and Mydoom.B worms.
In addition it will use the same exploits as the original Welchi variant,
information about those can be found from the Welchi description:
http://www.f-secure.com/v-descs/welchi.shtml
Detection in F-Secure Anti-Virus was published on February 12th,
2004 in update:
Version=2004-02-12_01
Description:
Katrin Tocheva, Mikko Hypponen February 12th, 2004
Technical details:
Ero Carrera, February 16th, 2004
