Apple just rolled out iOS 4.3.4 update for iPhone, iPod touch and iPad. This update from Apple will most probably fix the JailbreakMe PDF vulnerability patch, and thus all those who rely on JailbreakMe should avoid to update to iOS 4.3.4. So, we have this tutorial about how to downgrade iOS 4.3.4 to 4.3.3 and Verizon iOS 4.2.9 to 4.2.8
Actually Apple has described the technical fixes already as:
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.
iOS 4.3.4 Software Update
Fixes security vulnerability associated with viewing malicious PDF files.
Direct Download Links for iOS 4.3.4 (Official from Apple)

I would repeat it here again that those who rely on Jailbreak should stay from iOS 4.3.4 especially iPad 2 users as they can lose their Jailbreak by updating to iOS 4.3.4. On the other hand, Apple also released an update of iOS 4.2.9 for Verizon iPhone users which offers the same changes.
In between all the hussle of iOS 5 Betas, I believe this update is no good, obviously. It was even said by Comex
Now indeed you might want to downgrade your iPhone from iOS 4.3.4 to iOS 4.3.3 and same for the Verizon iPhone users downgrading it from iOS 4.2.9 to iOS 4.2.8
NOTE: This guide will only work if you have shsh blobs saved for the particular firmware you are downgrading too.
Step 1: Download old iOS’s firmware to which you want to downgrade.
Step 2: If you are a Windows user, then navigate to the following folder “C:\Windows\System32\drivers\etc”
OR if you are a mac OS X user, you can get to “/etc/” directory by going through “Go –> Go to Folder” from Finder.
Step 3: Look for the file name hosts and open it with Notepad in windows and mac users should look for TextEdit.
Step 4: Now add this following line at the bottom of the file. “74.208.10.249 gs.apple.com”

That’s it. Save this file and proceed.
Step 5: Get your iPhone, plug it in and lets put your iPhone into DFU mode.
- Turn off your phone.
- Now press Power button and as soon as you seen Apple Logo, press Home button while keeping pressed Power button too.
- Keep holding down both button for about 10 seconds.
- After 10 sec, release Power button but keep holding Home button until iTunes recognizes your iPhone. You should keep the PC volume high to hear New Device Detection sound.
- Let go the Home button. At this point your iPhone screen should be blank (black in color).
Step 6: Here, iTunes will alert you that “iTunes has detected an iPhone in recovery mode. You must restore it before it can be used.” Click okay
Step 7: Now, it time for us to restore the firmware – Hold down the “SHIFT” key (windows)/ “ALT”key (Mac) and click on “Restore“
Step 8: Wait for the restore to finish and you will then have a sigh of relief.
If you face any bugs or errors, feel free to comment and we will help you out.
Editor’s Note: Some people have faced problems with error 1013 when they downgrade from ios 4.3 to 4.2.1. Here is a video, suggested by a reader, that will help you bypass that error.
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