Jailbreak (S5L8920+)

When the iPhone 3GS was initially released, Apple did not have enough time to fix the 0x24000 Segment Overflow in the S5L8920. However, in order to flash an exploited LLB and jailbreak the iPhone 3GS, one of the following needed to be done:

• Find a new iBoot exploit every time a new firmware is out.
• Find a way to bypass the ECID checks.
• Use a bootrom exploit that allows unsigned code execution via USB.

Newer devices (iPhone 3GS with new bootrom, iPod touch 3G, and subsequent devices) are no longer vulnerable to the 0x24000 Segment Overflow exploit. Many of them are susceptible to geohot's bootrom exploit (originally found in limera1n), which allows unsigned code execution over USB. Even newer devices, starting with the iPad 2, have no bootrom exploits to run unsigned code at all.

ECID

Apple added a new tag to the IMG3 File Format called ECID. The ECID is unique to each phone, and its signature is being checked. With this method, Apple attempts to block downgrades once newer firmware becomes available, unless you have a dump of your old firmware's unique IMG3 or signed certificate. Therefore, iBoot exploits won't be so useful for tethered jailbreaks, because such exploits will be closed in new firmwares. [1].

The issue with this is that, even with the 0x24000 Segment Overflow still in bootrom, an iBoot exploit was still needed to actually flash the exploited LLB. Apple uses this ECID stuff to block downgrading iBoot to a vulnerable version. It was resolved when Geohot released his limera1n tool, which used a bootrom exploit to upload an unsigned iBoot. Still the problem remains with newer devices with 0x24000 fixed - tampering with firmware makes such jailbreak tethered unless some other exploit is used.

There are methods to help keep your downgrading ability, though.

• If it was cached prior to 3.1's release, 3GS owners were able save a file which contains the signature of the 3.0 iBSS containing their ECID, using the purplera1n website. A tool has not been created to incorporate this file into a fully signed iBSS, however.
• Saurik's servers are actively caching the necessary files. Instructions to use the servers are included.
• The SHSH associated with an ECID can be also saved by running TinyUmbrella. TinyUmbrella allows the user to restore to whatever version is associated with that SHSH file permanently. This is based on the aforementioned service Saurik provides remotely from his server(s).

Jailbreak tools

Apple TV 2G

Jailbreak Tool	Works with firmware...
	4.1	4.2	4.2.1	4.3
redsn0w	No	No	No	No
limera1n	no package management GUI	No	No	No
sn0wbreeze	no package management GUI	No	No	No
greenpois0n	no package management GUI	No	RC6	No
PwnageTool	no package management GUI	Restore from a custom firmware with unofficial bundle1	4.2	No
Seas0nPass	No	No	Yes	No

¹ Tethered jailbreak.

iPad

Jailbreak Tool	Works with firmware...
	3.2	3.2.1	3.2.2	4.2.1	4.3
Spirit	Yes	No	No	No	No
Star	Yes	Yes	No	Yes	No
limera1n	No	No	Yes	No	No
greenpois0n	No	No	RC4 and earlier	RC5	No
redsn0w	No	No	0.9.6b2	0.9.6rc81 or 0.9.7b61 2	No
PwnageTool	No	No	4.1-4.1.3	4.2	No
sn0wbreeze	No	No	2.1	2.2	No

¹ Tethered jailbreak.

² If SHSHs were saved for iOS 4.2b3 and if you have a developer access to its IPSW, Jailbreak Monte can be used.

iPad 2

Jailbreak Tool	Works with firmware...
	4.3

iPhone 3GS

Jailbreak Tool	Works with firmware...
	3.0	3.0.1	3.1	3.1.2	3.1.3	4.0	4.0.1	4.0.2	4.1	4.2.1	4.3
purplera1n	Yes	No	No	No	No	No	No	No	No	No	No
redsn0w	0.8	0.8	0.9.21 or 0.9.31	0.9.21 or 0.9.31	No	No	No	No	0.9.6b2	0.9.6rc81	No
blackra1n	No	No	Yes1	Yes1	No	No	No	No	No	No	No
Spirit	No	No	No	Yes	Yes	No	No	No	No	No	No
Star	No	No	No	Yes	Yes	Yes	Yes	No	No	No	No
PwnageTool	No	No	Restore from a custom firmware2	3.1.42	Restore from a custom firmware2		Restore from a custom firmware with unofficial firmware bundle2		4.1-4.1.3	4.2	No
sn0wbreeze	No	No	No	1.42 or 2.0.21 2	1.5.12 or 2.0.21 2	1.71 2 or 2.0.21 2	2.0.21 2		2.1	2.2	No
limera1n	No	No	No	No	No	Yes	Yes	Yes	Yes	No	No
greenpois0n	No	No	No	No	No	No	No	No	RC4 and earlier	RC5	No

¹ Tethered jailbreak on devices with the new bootrom.

² Only applicable for devices with the old bootrom. Requires the device to have signature checks disabled (pwned).

³ Requires an unofficial firmware bundle.

iPhone 4

Jailbreak Tool	Works with firmware...
	4.0	4.0.1	4.0.2	4.1	4.2.1	4.3
Star	Yes	Yes	No	No	No	No
limera1n	Yes	Yes	Yes	Yes	No	No
greenpois0n	No	No	No	RC4 and earlier	RC5	No
redsn0w	No	No	No	0.9.6b2	0.9.6rc81 or 0.9.7b61 2	No
PwnageTool	No	No	No	4.1-4.1.3	4.2	No
sn0wbreeze	No	No	No	2.1	2.2	No

¹ Tethered jailbreak.

² If SHSHs were saved for iOS 4.2b3 and if you have a developer access to its IPSW, Jailbreak Monte can be used.

iPod touch 3G

Jailbreak Tool	Works with firmware...
	3.1.1	3.1.2	3.1.3	4.0	4.0.2	4.1	4.2.1	4.3
blackra1n	Yes1	Yes1	No	No	No	No	No	No
redsn0w	0.9.21 or 0.9.31	0.9.21 or 0.9.31	No	No	No	0.9.6b2	0.9.6rc81	No
Spirit	No	Yes	Yes	No	No	No	No	No
Star	No	Yes	Yes	Yes	No	No	No	No
sn0wbreeze	No	2.0.21	2.0.21	1.71 or 2.0.21	2.0.21	2.1	2.2	No
limera1n	No	No	No	Yes	Yes	Yes	No	No
greenpois0n	No	No	No	No	No	RC4 and earlier	RC5	No
PwnageTool	No	No	No	No	No	4.1-4.1.3	4.2	No

¹ Tethered jailbreak.

iPod touch 4G

Jailbreak Tool	Works with firmware...
	4.1 (both builds)	4.2.1	4.3
limera1n	Yes	No	No
redsn0w	0.9.4b2	0.9.6rc81 or 0.9.7b61 2	No
greenpois0n	RC4 and earlier	RC5	No
PwnageTool	4.1-4.1.3	4.2	No
sn0wbreeze	2.1	2.2	No

¹ Tethered jailbreak.

² If SHSHs were saved for iOS 4.2b3 and if you have a developer access to its IPSW, Jailbreak Monte can be used.