Apple has released iOS 4.3.4 which is supposed to fix an issue that allows jailbreaking an iOS 4.3.3 device through a PDF vulnerability. Apple describes the technical fixes in a  support document:
Impact: Viewing a maliciously crafted PDF file may lead to an unexpected application termination or arbitrary code execution
Description: A buffer overflow exists in FreeType’s handling of TrueType fonts. Viewing a maliciously crafted PDF file may lead to an unexpected application termination or arbitrary code execution.
Users who have jailbroken their devices using JailbreakMe will obviously need to stay away from the update if they want to keep Cydia and other installed jailbreak tweaks.
Direct links for iOS 4.3.4:
| device | current version | date found |
|---|---|---|
| AppleTV(2G) (AppleTV2,1) | 4.2.2 (8F305) | 05/11/2011 16:06:01 |
| iPad (iPad1,1) | 4.3.4 (8K2) | 07/15/2011 13:26:01 |
| iPad2,1 (iPad2,1) | 4.3.4 (8K2) | 07/15/2011 13:26:01 |
| iPad2,2 (iPad2,2) | 4.3.4 (8K2) | 07/15/2011 13:26:01 |
| iPad2,3 (iPad2,3) | 4.3.4 (8K2) | 07/15/2011 13:26:01 |
| iPhone (iPhone1,1) | 3.1.3 (7E18) | 04/08/2010 21:05:48 |
| iPhone3G (iPhone1,2) | 4.2 (8C148) | 11/22/2010 13:08:57 |
| iPhone3GS (iPhone2,1) | 4.3.4 (8K2) | 07/15/2011 13:26:01 |
| iPhone4 (iPhone3,1) | 4.3.4 (8K2) | 07/15/2011 13:26:01 |
| iPhone4(vz) (iPhone3,3) | 4.2.9 (8E501) | 07/15/2011 13:26:01 |
| iPodTouch(2G) (iPod2,1) | 4.2 (8C148) | 11/22/2010 13:08:57 |
| iPodTouch(3G) (iPod3,1) | 4.3.4 (8K2) | 07/15/2011 13:26:01 |
| iPodTouch(4G) (iPod4,1) | 4.3.4 (8K2) | 07/15/2011 13:26:01 |