A total of 69 bugs have been fixed in the WebKit framework. This includes 62 memory corruption bugs, five multiple cross-origin bugs and two cross-origin bugs pertaining to content drag-and-drop as well as cookies. Other bug-fixes include patches to the inbuilt VPN (which addresses a format string vulnerability that could cause arbitrary code execution), as well as updates to Safari, Siri and the iOS kernel.
Several passcode lock bypass issues in iOS 5.0 have also been addressed, mitigating an issue that could allow a person with physical access to the device to bypass the screen lock. Issues in libresolv, handling of HFS catalogue files and CFNetwork modules have also been patched, which according to Apple could otherwise lead to the ‘disclosure of sensitive information through a maliciously crafted website,’.
A complete list of changes can be found at this Apple security advisory. This update is available over the air or via iTunes, which has also seen an update to v10.6 to avoid man-in-the-middle attack scenarios while accessing the Apple App store. The iOS 5.1 update can be found here, and you can get information on updating your specific Apple device here.