Apple has just pushed out iOS 5.1.1, which mainly addresses bugs like "unable to purchase" alerts and HDR problems some users have been encountering. The update weighs in at a light 54.5MB for a Verizon iPhone 4S, and comes about two months after the release of iOS 5.1, which included Japanese language support for Siri, the ability to delete photos from Photo Stream, and a redesigned camera app.

Here's the full release log:

  • Improves reliability of using HDR option for photos taken using Lock Screen shortcut.
  • Addresses bugs that could prevent the new iPad from switching between 2G and 3G networks.
  • Fixes bugs that affected AirPlay video playback in some circumstances.
  • Improved reliability for syncing Safari bookmarks and Reading List.
  • Fixes an issue where "Unable to Purchase" alert could be displayed after successful purchase.

The update is available now via the Software Update panel inside iOS's Settings app.

Update: Apple has now detailed the security contents of the update. 5.1.1 addresses three different vulnerabilities, one in Safari and two in WebKit itself, but if you'd like to read the full details yourself, you can visit the company's support document.