AT+XEMN Heap Overflow

AT+XEMN is a command on baseband 5.11.07 (pushed out with the 3.1 release), which when exploited correctly, causes a heap overflow allowing the crash to be moulded into an injection vector. This injection vector can then be used to inject an unlocking payload to provide a software SIM unlock on the official 3.1(.2) firmware running 5.11.07.

Credit

• Vulnerability: Oranav (July) and iH8sn0w (September) (discovered independently)
  
• Exploit: geohot

Implementation

This exploit is used in blacksn0w.

Exception Dump

+XLOG: Exception Number: 1
Trap Class:     0xDDDD  (SW GENERATED TRAP)
Identification: 140 (0x008C)
Date: 22.10.2009
Time: 00:30
File: atform/text/_malloc.c
Line: 1036
Logdata:
 2E 0C 76 ED 40 14 31 64 61 74 63 3A 31 00 64 63   ..v.@.1datc:1.dc
 20 44 F4 E9 20 20 20 20 20 20 20 20 20 20 20 20    D..            
 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20                   
 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20                   
 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20                   
 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20                   
 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20                   
 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20                   
 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20                   
 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20                   
 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20                   
 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20                   
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Timeline

July 2009

• Oranav discovers this crash and gives it to the iPhone Dev Team.
• Upon initial investigation, The iPhone Dev Team, mistakenly concludes that the crash is non-exploitable.

September 2009

• iH8sn0w discovered this command independently but kept it a secret for about a month. [1]

October 2009

• When the iPhone Dev Team stated that iH8sn0w did not have an unlock, he posted the command on Twitter. [2]
• Shortly after, Oranav posted his Hash from July. [3]
• MuscleNerd tells iHacker that the crash was received awhile ago and is thought to be non-exploitable. [4][5]
• Geohot attempts to exploit this crash, but intially also finds it to be non-exploitable. [6]
• Geohot does more investigation and discovers that this crash is indeed exploitable, and that it's a heap overflow. [7]
• Geohot achieves arbitrary code execution and begins work on unlock which will be called blacksn0w. [8]
• Geohot posts a video of an unlocked 5.11.07 device. [9]

November 2009

• Geohot releases blacksn0w to the masses.