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Virus Name Risk Assessment
W32/Sasser.worm.d Corporate User : Low
Home User : Low
Virus Information
Discovery Date: 05/03/2004
Origin: Unknown
Length: 16,384 bytes (packed)
Type: Virus
SubType: Internet Worm
Minimum DAT: 4357 (05/05/2004)
Updated DAT: 4357 (05/05/2004)
Minimum Engine: 4.2.40
Description Added: 05/03/2004
Description Modified: 05/03/2004 7:00 AM (PT)
Description Menu
Virus Characteristics
Symptoms
Method Of Infection
Removal Instructions
Variants / Aliases
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Virus Characteristics:
AVERT has received a new variant of W32/Sasser.worm .
The previous variants of this self-executing worm spread by exploiting a Microsoft Windows vulnerability [MS04-011 vulnerability (CAN-2003-0533)].
This variant of the worm is intended to spread with the following file name:
SKYNETAVE.EXE
Unlike many recent worms, this virus does not spread via email. No user intervention is required to become infected or propagate the virus further. The worm works by instructing vulnerable systems to download and execute the viral code.
Note: Infected systems should install the Microsoft update to be protected from the exploit used by this worm. See:
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Symptoms
The virus copies itself to the Windows directory as SKYNETAVE.EXE and creates a registry run key to load itself at startup
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\
CurrentVersion\Run "skynetave.exe" = %WinDir%\skynetave.exe
As the worm scans random IP addresses it listens on successive TCP ports starting at 1068. It also acts as an FTP server on TCP port 5554, and creates a remote shell on TCP port 9996.
A file named win2.log is created on the root of the C: drive. This file contains an IP address together with the number of machines infected.
Copies of the worm are created in the Windows System directory as #_up.exe. (Where '#' represents a string 4 or 5 digits.)
Examples
c:\WINDOWS\system32\26347_up.exe
c:\WINDOWS\system32\5157_up.exe
A side-effect of the worm is for LSASS.EXE to crash, by default such a system will reboot after the crash occurs. The following Window may be displayed:
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Method Of Infection
This worm spreads by exploiting a recent Microsoft vulnerability, spreading from machine to machine with no user intervention required.
The propagation mechanism is akin to that for previous variants:
the worm scans random IP addresses for exploitable systems. When one is found, the worm exploits the vulnerable system, by overflowing a buffer in LSASS.EXE.
It creates a remote shell on TCP port 9996.
Next it creates an FTP script named cmd.ftp on the remote host and executes it. The specified DATs contain detection for this FTP script as W32/Sasser.worm!ftp .
the FTP script instructs the target victim to download and execute the worm (with the filename #_up.exe as mentioned above) from the infected host.
The infected host accepts this FTP traffic on TCP port 5554.
The worm spawns multiple threads, some of which scan the local class A subnet, others the class B subnet, and others completely random subnets. The destination port is TCP 445.
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Recuerdese que tras ejecutar la utilidad indicada, version 1.1, debe conectarse a
saludos
ms, 03-05-2004
msc hotline sat Virus Research Engineer