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The worm was first noticed and started spreading on August 11, 2003. The rate that it spread increased until the number of infections peaked on August 13, 2003. Filtering by ISPs and widespread publicity about the worm curbed the spread of Blaster.
On August 29, 2003, Jeffrey Lee Parson, an 18-year-old from Hopkins, Minnesota, was arrested for creating the B variant of the Blaster worm; he admitted responsibility and was sentenced to an 18-month prison term in January 2005.
According to court papers, the original Blaster was created after security researchers from the Chinese group Xfocus reverse engineered the original Microsoft patch that allowed for execution of the attack.
The worm spread by exploiting a buffer overflow discovered by the Polish security research group Last Stage of Delirium in the DCOM RPC service on the affected operating systems, for which a patch had been released one month earlier in MS03-026 and later in MS03-039. This allowed the worm to spread without users opening attachments simply by spamming itself to large numbers of random IP addresses. Four versions have been detected in the wild.
The worm was programmed to start a SYN flood against port 80 of windowsupdate.com if the system date is after August 15th and before December 31st and after the 15th day of other months, thereby creating a distributed denial of service attack (DDoS) against the site. The damage to Microsoft was minimal as the site targeted was windowsupdate.com, rather than windowsupdate.microsoft.com to which the former was redirected. Microsoft temporarily shut down the targeted site to minimize potential effects from the worm.
The worm's executable contains two messages. The first reads:
I just want to say LOVE YOU SAN!!soo much
This message gave the worm the alternative name of Lovesan. The second reads:
Billy Gates why do you make this possible ? Stop making money
and fix your software!!
The worm also creates the following registry entry so that it is launched every time Windows starts:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\windows auto update=msblast.exe
Although the worm can only spread on systems running Windows 2000 or Windows XP (32 bit) it can cause instability in the RPC service on systems running Windows NT, Windows XP (64 bit), and Windows Server 2003. In particular, the worm does not spread in Windows Server 2003 because Windows Server 2003 was compiled with the /GS switch, which detected the buffer overflow and shut the RPCSS process down. When infection occurs, the buffer overflow causes the RPC service to crash, leading Windows to display the following message and then automatically reboot, usually after 60 seconds.
|“||System Shutdown: |
This system is shutting down. Please save all work in progress and log off. Any unsaved changes will be lost. This shutdown was initiated by NT AUTHORITY\SYSTEM
Time before shutdown: hh:mm:ss
Windows must now restart because the Remote Procedure Call (RPC) Service terminated unexpectedly.
This was the first indication many users had an infection; it often occurred a few minutes after every startup on compromised machines. A simple resolution to stop countdown is to run the "shutdown -a" command in the Windows command line, causing some side effects such as an empty (without users) Welcome Screen. The Welchia worm had a similar effect. Months later, the Sasser worm surfaced, which caused a similar message to appear.