Apple yesterday patched three vulnerabilities in Safari, including one in the Windows version that quashed a bug Microsoft said individual developers had to fix themselves.
Apple and Mozilla are the only major browser makers who have patched what most researchers have called "DLL load hijacking."
In the updates to Safari 5.0.2 and Safari 4.1.2, Apple addressed a problem shared by scores of Windows applications that can be exploited by duping users into downloading innocent files.
Last month, HD Moore, chief security officer at Rapid7 and the creator of the open-source Metasploit hacking toolkit, announced that several dozen Windows programs were flawed because they improperly loaded code libraries -- dubbed "dynamic-link libraries," or "DLLs" -- and so gave hackers a way to commandeer a PC by tricking the application into calling on a malicious DLL.
Other researchers later estimated that more than 200 different Windows programs could be exploited, including Safari, Opera, Mozilla's Firefox and Google's Chrome.
Mozilla patched the DLL load hijacking vulnerability Tuesday in a 15-patch Firefox security update.
"While I don't see such patching as a who's-first competition, the users would be better off if it actually was," said Mitja Kolsek, CEO of Acros Security, the Slovenian security firm that Apple credited with reporting the Safari issue.
Apple's problem, however, goes beyond DLL hijacking, Kolsek added in an e-mail reply to questions today. "This is a binary planting issue, just not with a DLL but with an EXE," he said.
"Binary planting," Acros' term for the bug, indicates that the vulnerability extended to bogus .exe files as well as DLLs. Hackers can exploit the flaw in much the same way as in DLL load hijacking, by tricking applications into loading malicious .exe files.
Not all Windows applications vulnerable to DLL load hijacking are also susceptible to rogue .exe file loading, but Safari was -- until Apple issued its Tuesday patches.
Kolsek said Acros would publish more information on the Safari vulnerability later today on its Web site.
Apple also patched a pair of bugs in all versions of Safari, including the more popular Mac edition yesterday. Those two flaws, said Apple in its accompanying advisory, were in WebKit, the open-source browser engine that powers not only Safari, but also Chrome. Both bugs could be exploited by hackers through "drive-by" attacks that launch as soon as a victim browses to a malevolent Web site.
But although Apple's plugged several Safari holes, it still faces others. An unpatched vulnerability in the QuickTime plug-in used by Microsoft's Internet Explorer has yet to be addressed.
That bug went public last week when Spanish researcher Ruben Santamarta published information and attack code for a flaw he traced to Apple's failure to clean up code after developers dropped the "_Marshaled_pUnk" function. Santamarta wasn't the first to notice the QuickTime vulnerability: The flaw was reported to Apple over two months ago by HP TippingPoint's Zero Day Initiative (ZDI) bug bounty program.
Exploits for the QuickTime bug are now actively being used by hackers, Websense said Tuesday.
Safari 5.0.2 can be downloaded from Apple's site for Mac OS X 10.5 (Leopard), Mac OS X 10.6 (Snow Leopard), Windows XP, Windows Vista and Windows 7. Safari 4.1.2, meanwhile, runs on those operating systems as well as Mac OS X 10.4 (Tiger).
Mac OS X users will be notified of the new version automatically, while Windows users already running Safari will be alerted by the Apple Software Update tool.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer or subscribe to Gregg's RSS feed . His e-mail address is email@example.com.