The update comes less than two weeks after iOS 4.3.4 was released. It is available for the GSM iPhone 4, iPhone 3GS, iPad 2, iPad, and third- and fourth-generation iPod touch.
Also released on Monday was iOS 4.2.10 for the CDMA iPhone, available on Verizon's network.
The previous iOS update was released on July 15. It patched a security hole related to viewing PDFs in the Mobile Safari Web browser, an exploit that had been utilized by hackers to "jailbreak" the iPhone and iPad.
Though security fixes have been issued, Apple is not expected to add any major new features to iOS 4. The company is focused on delivering the next-generation version of its mobile operating system, iOS 5, to users this fall.
iOS 5 is currently in beta and is being tested by developers who write software for iPhones and iPads. The fourth beta of iOS 5 was issued to developers last Friday.