Glow for FB is an AppStore program that hooks into the OSX Notification system (Mountain Lion onward) and notifies you of events on your facebook account. The only check is obviously the receipt file from the AppStore, given that this application does not even have a trial.

Cracking Glow thus involves jumping over all the possible error messages that check the receipt of the application. The function that performs these checks can be found about 0x10001be18 and starts like this:

                                       ; Basic Block Input Regs: rbx rbp rsi rdi r12 r13 r14 r15 -  Killed Regs: rax rdx rbx rsp rbp rsi rdi r12 r14 r15
000000010001be18 55                              push       rbp                           ; XREF=0x100008633
000000010001be19 4889E5                          mov        rbp, rsp
000000010001be1c 4157                            push       r15
000000010001be1e 4156                            push       r14
000000010001be20 4155                            push       r13
000000010001be22 4154                            push       r12
000000010001be24 53                              push       rbx
000000010001be25 4881ECA8000000                  sub        rsp, 0xa8
000000010001be2c 4989F7                          mov        r15, rsi
000000010001be2f 4189FC                          mov        r12d, edi
000000010001be32 488B0557420100                  mov        rax, qword [ds:imp___got____stack_chk_guard]
000000010001be39 488B00                          mov        rax, qword [ds:rax]
000000010001be3c 488945D0                        mov        qword [ss:rbp-0x0+var_m48], rax
000000010001be40 488B3521F90100                  mov        rsi, qword [ds:objc_sel_mainBundle] ; @selector(mainBundle)
000000010001be47 488B3D0A090200                  mov        rdi, qword [ds:bind__OBJC_CLASS_$_NSBundle]
000000010001be4e FF158C420100                    call       qword [ds:imp___got__objc_msgSend]
000000010001be54 4889C7                          mov        rdi, rax
000000010001be57 E854210000                      call       imp___stubs__objc_retainAutoreleasedReturnValue
000000010001be5c 4889C3                          mov        rbx, rax
000000010001be5f 488D35FA060200                  lea        rsi, qword [ds:objc_msg_respondsToSelector_] ; @selector(respondsToSelector:)
000000010001be66 488B1503060200                  mov        rdx, qword [ds:objc_sel_appStoreReceiptURL] ; @selector(appStoreReceiptURL)
000000010001be6d 4889DF                          mov        rdi, rbx
000000010001be70 FF15EA060200                    call       qword [ds:objc_msg_respondsToSelector_] ; @selector(respondsToSelector:)
000000010001be76 4188C6                          mov        r14L, al
000000010001be79 4889DF                          mov        rdi, rbx
000000010001be7c E817210000                      call       imp___stubs__objc_release
000000010001be81 4584F6                          test       r14L, r14L

Browsing the function you will observe that you will have instances where versious checks are performed to determine whether the receipt is legitimate. All these checks have to be skipped; jumped over by turing jes, jnes, and so on into jumps. For example, the first instance where a jump is necessary is right after the function starts:

000000010001bf18 E924000000                      jmp        0x10001bf41
000000010001bf1d 90                              nop        
000000010001bf1e 90                              nop        
000000010001bf1f 90                              nop        
000000010001bf20 90                              nop        
000000010001bf21 488B3D70090200                  mov        rdi, qword [ds:bind__OBJC_CLASS_$_NSException]
000000010001bf28 488D15D1530200                  lea        rdx, qword [ds:cfstring_MacAppStore_Receipt_Validation_Error] ; @"MacAppStore Receipt Validation Error"
000000010001bf2f 488D0D0A570200                  lea        rcx, qword [ds:cfstring_Failed_to_check_bundle_ID_] ; @"Failed to check bundle ID."
000000010001bf36 4531C0                          xor        r8d, r8d
000000010001bf39 30C0                            xor        al, al
000000010001bf3b FF159F410100                    call       qword [ds:imp___got__objc_msgSend]

The jump at 0x10001bf18 skips the validation error and lets the program carry on. The next instance is then:

000000010001bff5 E924000000                      jmp        0x10001c01e
000000010001bffa 90                              nop        
000000010001bffb 90                              nop        
000000010001bffc 90                              nop        
000000010001bffd 90                              nop        
000000010001bffe 488B3D93080200                  mov        rdi, qword [ds:bind__OBJC_CLASS_$_NSException]
000000010001c005 488D15F4520200                  lea        rdx, qword [ds:cfstring_MacAppStore_Receipt_Validation_Error] ; @"MacAppStore Receipt Validation Error"
000000010001c00c 488D0D8D550200                  lea        rcx, qword [ds:cfstring_Failed_to_validate_bundle_signature__Create_a_static_code] ; @"Failed to validate bundle signature: Create a static code"
000000010001c013 4531C0                          xor        r8d, r8d
000000010001c016 30C0                            xor        al, al
000000010001c018 FF15C2400100                    call       qword [ds:imp___got__objc_msgSend]

Then the next:

000000010001c040 E935000000                      jmp        0x10001c07a
000000010001c045 90                              nop        
000000010001c046 90                              nop        
000000010001c047 90                              nop        
000000010001c048 90                              nop        
000000010001c049 4885FF                          test       rdi, rdi
000000010001c04c 7405                            je         0x10001c053
000000010001c04e E8E71F0000                      call       imp___stubs__CFRelease
000000010001c053 488B3526040200                  mov        rsi, qword [ds:objc_sel_raise_format_] ; @selector(raise:format:) XREF=0x10001c04c
000000010001c05a 488B3D37080200                  mov        rdi, qword [ds:bind__OBJC_CLASS_$_NSException]
000000010001c061 488D1598520200                  lea        rdx, qword [ds:cfstring_MacAppStore_Receipt_Validation_Error] ; @"MacAppStore Receipt Validation Error"
000000010001c068 488D0D71550200                  lea        rcx, qword [ds:cfstring_Failed_to_validate_bundle_signature__Create_a_requirement] ; @"Failed to validate bundle signature: Create a requirement"
000000010001c06f 4531C0                          xor        r8d, r8d
000000010001c072 30C0                            xor        al, al
000000010001c074 FF1566400100                    call       qword [ds:imp___got__objc_msgSend]

and this carries on for quite a while, up to the last required sequence:

000000010001c8a5 E924000000                      jmp        0x10001c8ce
000000010001c8aa 90                              nop        
000000010001c8ab 90                              nop        
000000010001c8ac 90                              nop        
000000010001c8ad 90                              nop        
000000010001c8ae 488B3DE3FF0100                  mov        rdi, qword [ds:bind__OBJC_CLASS_$_NSException]
000000010001c8b5 488D15444A0200                  lea        rdx, qword [ds:cfstring_MacAppStore_Receipt_Validation_Error] ; @"MacAppStore Receipt Validation Error"
000000010001c8bc 488D0D7D4A0200                  lea        rcx, qword [ds:cfstring_Failed_to_check_receipt_hash_] ; @"Failed to check receipt hash."
000000010001c8c3 4531C0                          xor        r8d, r8d
000000010001c8c6 30C0                            xor        al, al
000000010001c8c8 FF1512380100                    call       qword [ds:imp___got__objc_msgSend]

The last jne before the function returns can be left alone:

000000010001c948 7573                            jne        0x10001c9bd
                                       ; Basic Block Input Regs: rbx -  Killed Regs: rax rbx rsp rbp r12 r13 r14 r15
000000010001c94a 89D8                            mov        eax, ebx
000000010001c94c 4881C4A8000000                  add        rsp, 0xa8
000000010001c953 5B                              pop        rbx
000000010001c954 415C                            pop        r12
000000010001c956 415D                            pop        r13
000000010001c958 415E                            pop        r14
000000010001c95a 415F                            pop        r15
000000010001c95c 5D                              pop        rbp
000000010001c95d C3                              ret        

There are quite a few of these steps, just remember than given the top-down execution, the function must avoid those error sequences and carry on till it reaches the ret.

That is it for Glow for FB at version 1.0.7. :-)


cracks/glow_for_fb.txt ยท Last modified: 2017/02/22 18:30 (external edit)

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