Apple Tuesday issued its fourth security Mac OS X update of the year, patching 25 vulnerabilities, nearly half of them considered critical. The company also updated Safari for the Mac to plug a hole already fixed in the Windows version of the browser and released an update to bring the OS to version 10.5.4.

Security Update 2008-004, which follows its predecessor by about a month, fixes flaws in a dozen components of Mac OS X 10.4 (aka Tiger) and 10.5 (Leopard), ranging from Alias Manager and the Dock to VPN and WebKit. Apple labeled 11 of the 25 vulnerabilities with its "arbitrary code execution" tag, thus slotting them into a category that vendors which rate threats would peg as "critical."

Over half of the vulnerabilities were in open-source code and components that Apple bundles or integrates with its own, a not-so-unusual position for the Cupertino, Calif. company to be in, according to Andrew Storms, director of security operations at nCircle Network Security Inc. "There's a substantial amount of software [patched] in the update that Apple is not directly responsible for," said Storms. "That will continue to be a problem for Apple, and its only solution will be to turn about updates sooner."

Security Update 2.008-004 quashed multiple bugs in Ruby, the object-oriented open-source scripting language, and in Apache Tomcat, another open-source component that provides a server environment for running Java code. Five of the six Ruby vulnerabilities were reported week before last to the Ruby developers by Apple's own security team.

"By Apple's standards, getting the Ruby fixes into this update is pretty darn fast," Storms said.

The nine Tomcat vulnerabilities, meanwhile, affect only Mac OS X 10.4; Leopard is bundled with a more up-to-date version of Tomcat. According to Apple's description, the most serious of the Tomcat flaws could enable cross-site scripting attacks, a popular vector often used by identity thieves and phishers.

Several of today's patches address problems only in the newest version of Apple's operating system, including ones in Leopard's Dock and virtual private network (VPN) implementation.

The bug in Mac OS X 10.5's Dock could be used by someone with physical access to the computer -- someone in the same office, for example -- to bypass the password requirement that kicks in when the machine comes out of sleep or exits a screensaver. "This update addresses the issue by disabling hot corners when the screen lock is active," today's security bulletin read.

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