Virus Profile: W32/Sasser.worm.e

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Virus Profile information details
Risk Assessment: Home Low-Profiled | Corporate Low-Profiled
Date Discovered: 5/8/2004
Date Added: 5/8/2004
Origin: Unknown
Length: 15,872 byte
15,873 bytes
Type: Virus
Subtype: Internet Worm
DAT Required: 4359
Removal Instructions


This is a virus detection. Viruses are programs that self-replicate recursively, meaning that infected systems spread the virus to other systems, which then propagate the virus further. While many viruses contain a destructive payload, it's quite common for viruses to do nothing more than spread from one system to another.

Indication of Infection

The virus copies itself to the Windows directory as LSASSS.EXE and creates a registry run key to load itself at startup

    CurrentVersion\Run "lsasss.exe" = %WinDir%\lsasss.exe

The virus attempts to remove the following registry keys, used by various Bagle virus variants:

  • HKEY_CURRENT_USER\Software\Microsoft\Windows\
    CurrentVersion\Run "ssgrate.exe"
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\
    CurrentVersion\Run "drvsys.exe"
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\
    CurrentVersion\Run "Drvddll_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 1023, and creates a remote shell on TCP port 1022.

A file named ftplog.txt 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.)


  • 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:


The worm contains the following message:

1. Your computer is affected by the MS04-011 vulnerability
2. It can be that dangerous computer viruses similar
     the Blaster worm infect your computer
3. Please update your computer with the MS04-011 LSASS patch
    from the website
4. This is an message from the SkyNet Team for
     malicious activity prevention

Methods 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 1023.
  • Next it creates an FTP script named cmd.ftp on the remote host and executes it. Via the FTP script, the FTP.EXE application is used to retrieve the worm from the infected machine (port 1023) to the remote host. The worm is then executed.
  • 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 1023.

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 worm scans public ranges like and only if they are part of the local subnet. The destination port is TCP 445.


W32/Sasser.worm.g (SARC) 15,873 byte sample

Virus Characteristics

- Update June 11th 2004  --
A slighltly modified version of this variant has been reported. The file size is 15,873 bytes (+1 from original e variant). This sample is detected and cleaned as W32/Sasser.worm.e with the 4359 DATs or greater.

Analysis suggests that this sample has arisen from a W32/Pate infection of a W32/Sasser.worm.e sample, which has been cleaned by an AV product.

Note: the W32/Pate infection has been removed - the W32/Pate infection will not replicate. However, there are slight remnants of the infection remaining (eg. the added last PE section, containing only 1 byte after the clean) which account for the differences to the original W32/Sasser.worm.e sample.


- Update May 10th 2004  --
This threat has been deemed Low-Profiled due to media attention at the following site:


This Sasser variant is similar to W32/Sasser.worm.d , with the following exceptions:

  • This variant uses the filename lsasss.exe (15,872)
    NOTE: This filename was chosen to confuse people.  There is a valid file named lsass.exe
  • It creates a remote shell on TCP port 1022 rather than 9995
  • It uses the file c:\ftplog.txt rather than c:\win2.log
  • It uses FTP on TCP port 1023 instead of 5554
  • It attempts to disable Bagle variants by removing registry keys created by Bagle

This self-executing worm spread by exploiting a Microsoft Windows vulnerability [MS04-011 vulnerability (CAN-2003-0533)]

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:

All Users :
Use the specified DAT files for detection and removal.

Modifications made to the system Registry and/or INI files for the purposes of hooking system startup, will be successfully removed if cleaning with the recommended engine and DAT combination (or higher).

Additional Windows ME/XP removal considerations


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