W32SQLSlammerWorm

W32.SQLSlammer.Worm, commonly referred to as SQL Slammer, Sapphire, or by its antivirus name W32.SQLSlammer.Worm, was a fast-spreading computer worm that emerged in 2003. It targeted Microsoft SQL Server 2000 installations by exploiting a vulnerability in the SQL Server Resolution Service accessible via UDP port 1434. The worm is notable for its extremely compact size and rapid propagation.

The outbreak began on January 25, 2003, and the worm spread by scanning random Internet addresses and sending a single, small UDP packet to any vulnerable SQL Server instance. The payload, about 376 bytes in size, exploited a buffer overflow in the Resolution Service, causing infected hosts to launch new copies of the worm. Because the worm required no user interaction, it propagated autonomously and very quickly.

Impact and scope of the incident were substantial. The rapid spread caused significant network congestion and load, affecting Internet backbone traffic and many corporate networks. Estimates of infected hosts vary, but the outbreak is cited as infecting tens of thousands of machines within minutes, contributing to widespread performance degradation and outages in some environments.

Mitigation and remediation involved applying a security patch from Microsoft (MS03-039) that fixed the underlying vulnerability, as well as strengthening network defenses. Administrators were advised to patch affected systems, block UDP traffic to port 1434 where feasible, disable the SQL Server Resolution Service if it was not needed, and ensure updated antivirus signatures were in place. The SQL Slammer incident underscored the importance of timely patch management and network-level protections against fast-spreading, small-scale exploits.