Jailbreak

The term "jailbreak" is the process by which some form of arbitrary code execution (usually by spawning of an SSH shell) is obtained by exploiting the kernel (and other protections, such as AMFI, PAC, PPL, KPP, and KTRR - but these do not apply to every software version) of iOS, iPadOS, watchOS, tvOS, audioOS, or bridgeOS. It used to be done by patching /private/etc/fstab to mount the System partition as 'read-write'. This is entirely different from an unlock. Jailbreaking is the first action that must be taken before things like unofficial activation (hacktivation), and unofficial unlocking can be applied.

Older jailbreaks also included modifying the AFC service (used by iTunes to access the filesystem) to give full filesystem access from root. This was later updated to create a new service (AFC2) that allows access to the full filesystem.

Modern jailbreaks modifies kernel variable memory instead of outright patching the kernel, due to restrictions posed by KPP and KTRR, with the exception of checkm8-based jailbreaks.

Note: The legality of jailbreaking your device varies with each country/region. Wikipedia has a summary of legality for some countries.

Types of Jailbreaks
Tethered : The device must be booted using a computer every time, otherwise it won't boot at all. This type of jailbreak is uncommon. This is because, starting with the iPod touch 2 (new BR) and iPhone 3GS, Apple has signature checks for its bootchain, which includes LLB, iBoot, and the Kernel, meaning a custom bootchain cannot be loaded unless an exploit is used to patch these checks. Example of tethered jailbreaks are 4039, blackra1n, and orangesn0w.

Semi-tethered : The device must be jailbroken using a computer every time it's rebooted, otherwise it will boot in unjailbroken state. Examples of semi-tethered jailbreaks are opensn0w, geeksn0w, checkra1n, or palera1n. They are similar to tethered jailbreaks in how they jailbreak iOS, but they don't modify iOS' default bootchain - instead sending their own custom one.

Untethered : Untethered jailbreaks were originally how almost every jailbreak was - run the jailbreak once, and then you're jailbroken for life. They could be installed via Safari with JailbreakMe, or with a computer, using redsn0w, Absinthe, or Pangu. However, these types of jailbreaks started to die out in iOS 9.

Semi-untethered : Starting with iOS 9, it was no longer easy to make a fully untethered jailbreak, so devs instead created semi-untethered jailbreaks. These jailbreaks are run using an app which jailbreaks the device, but after a reboot, the app will need to be run again - otherwise the device will be unjailbroken. Examples of these are Home Depot, Meridian, unc0ver, Chimera, Taurine, or Dopamine. Due to Apple limitations, the app must be resigned every week (or every year with a paid developer account). Tools like ReProvision Reborn were created to automate this process. Additionally, with iOS versions compatible with TrollStore, it is possible to permanently sign the jailbreak app so it will never expire.

Semi-jailbreak
This type of jailbreak is like between untethered and semi-untethered jailbreak in which when the device reboots, it stays jailbroken, but the key differences are that even without patched kernel, jailbreak bootstrap works without PC required and the jailbreak bootstrap features are very limited since the kernel is not RW (not patched). To get access to jailbreak apps, run semi-jailbreak tool and with clicking the semi-jailbreak button it will add all jb installed apps to the screen thanks to uicache command provided by semi-jailbreak bootstrap.

Some semi-jailbreak tools are working on keeping apps on the screen even after reboots so that user don't need to open the app to access to all jb apps.

The only requirement is bug like CoreTrust v2 that is powerful enough to exploit CoreTrust and allow limited number of libraries and binaries (the bootstrap itself with/without jb apps) to work.

The things that are not supported in this type of jailbreak is:

1. Full Tweak Injection support (tweaks like AppSync Unified and similar that requires kernel rw and other bypasses will not work - that's why ElleKit cannot be used but it can be installed anyway, but it's not useable)

2. Using external terminals (many terminals are using kernel rw method to run session so only limited number of terminals, mostly provided by semi-jailbreak tools are supported)

3. Using real unpatched sudo and su (sudo and su are compiled in the way that they also requires other bypasses and kernel rw to work since root sessions and services are started in kernel rw, not in userspace - that's why most semi-jailbreak tools provides their custom versions of su and sudo that will run root sessions in userspace)

4. Executing custom LaunchDaemons (Every daemon/service execution was done via launchd binary provided by Apple and signed by Apple - that binary only allows platform binaries to run with those privileges - if the target binary are not platform binary signed by Apple, it will deny execution - CoreTrust bug cannot exploit this since kernel are checking and verify executions done by launchd binary. That also means that patching this binary directly without patching the kernel first will result in panic reboot)

The benefits of semi-jailbreaks are:

1. Since it doesn't patching the kernel the device is more stock and it's compatibility with apps and security will not be broken

2. No kernel panics can happen, much more safe for beginners

Semi jailbreak with kernel r/w
Due to restriction posed by KPP, KTRR, PPL, SPTM, TXM and PAC, having kernel r/w alone cannot achieve a jailbreak on arm64e devices. However, with the CoreTrust bypass, it's possible to implement most parts of the jailbreak.

The following that's not possible in a semi-jailbreak without kernel r/w are possible:

1. (Mostly) full tweak injection support - by using kernel r/w to overwrite /sbin/launchd, it is possible to remove various checks in launchd to allow custom binaries to be executed.

2. Using LaunchDaemons - also by removing restrictions in launchd.

3. Kernel panics can happen, though generally rare after initialization.

4. Tweak applications without reregistering them as a system app. (with xpcproxy hook to spawn an alternative executable)

Latest firmware and Jailbreak status
For other devices, firmware versions and jailbreak tools, see the versions list below.

Versions
Untethered or semi-untethered jailbreaks are shown with a green 'yes'. Tethered or semi-tethered jailbreaks will be stated in a yellow box. Beta Firmwares are not listed.


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