MacRumors.com

Security Update 2003-11-04 addresses a potential vulnerability with the Terminal application in Mac OS X v10.3 and Mac OS X Server v10.3 that could allow unauthorized access to a system.

Apple also released an Xcode update yesterday:

The Xcode Update addresses an issue in the Xcode IDE that could potentially lead to data corruption or the loss of files particularly when source files contain illegal characters. This update is strongly recommended for all Xcode users.

Both updates are available through the Mac OS X Software Update control panel. (The Xcode update only appears if you have Xcode installed).