The security document for iOS 9.3.4 lists just one security issue resolved: an IOMobileFrameBuffer memory corruption issue used by Pangu Team to facilitate their jailbreak.
Available for: iPhone 4s and later, iPad 2 and later, iPod touch (5th generation) and later
Impact: An application may be able to execute arbitrary code with kernel privileges
Description: A memory corruption issue was addressed through improved memory handling.
CVE-2016-4654: Team Pangu
If you are jailbroken or looking to jailbreak make sure you do not accidentally update to iOS 9.3.4 or you will lose the ability to jailbreak your device.
You can find instructions on how to jailbreak here.
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