Some users claimed that they cannot jailbreak the Apple devices that they bought recently with Redsn0w. There have been a lot of speculations and one is that Apple might have patched the limera1n exploit that has been used in Redsn0w to jailbreak the iOS 4.2.1 in newer iPhones, iPads and iPod Touches.
Limera1n was first introduced way back in October by Geohot as a jailbreaking tool for iOS 4.1 using a bootrom exploit. Since it was bootrom exploit or in the hardware level, it means that Apple could not stop the exploit from being used in existing iDevices and to prevent users from jailbreaking their gadgets. However, Apple can now prevent their newer iDevices from jailbroken by patching the bootrom exploit.
One user told in a forum that he believed that Apple already patched the exploit to newer iDevices. He said, “I made a trip to the Apple Store today to get an iPad for my old lady (Christmas present). She told me she’d love it jailbroken, so I sat down in front of my computer to redsn0w this 4.2.1 iPad. One problem–redsn0w 0.9.6b6 could not upload a pwned iBSS (hanged at the white screen on OS X, upload timed out and rebooted into jailed state with Windows). Furthermore, the device constantly stalls when attempting to dump its bootrom. This leads me to believe the injection vector used via USB has been patched in DFU mode. Case in point: Any iOS device with a serial number xx050 (this week) or higher might be unable to be jailbroken via the limera1n exploit. Slightly older devices may be invulnerable as well.”
You can find out if you can still jailbreak your iPhone, iPad or iPod Touch with limera1n by looking at the serial number to find out which week your iDevice was manufactured. The serial number can be found on the iTunes summary page or Settings App –> General –> About –> Serial Number. The first two digits of the serial number gives you the factory ID of where it was manufactured and the next three digits (Digits 3-4-5) tells you when it was manufactured.
Based on speculations, new iPhone, iPod Touch and iPad manufactured from the 50th week of 2010 may have the updated bootrom. This is not the first time that Apple did this to stay ahead in the cat and mouse chase with the jailbreaking community. October last year, Apple started shipping iPhone 3GS with newer bootrom to prevent jailbreaking.