Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/6c51a5ba17ffd317ad08541e20131ef3.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Agent.xs
Vulnerability: Insecure Permissions 
Description: The malware creates a hidden but insecure dir named "Recycler" under c:\ drive and grants change (C) permissions to the authenticated user group. It also drops an exe named "explorer.exe", standard users can rename the malware and reboot to disable it or replace with their own executable to escalate privileges when a privileged user logs on to the infected machine.
Type: PE32
MD5: 6c51a5ba17ffd317ad08541e20131ef3
Vuln ID: MVID-2021-0106
Dropped files: explorer.exe
Disclosure: 02/23/2021 


Exploit/PoC:
void main(void){
  
    puts("[+] Unhiding the malware to rename it...");
    system("attrib -h C:\\Recycler\\explorer.exe");
    system("RENAME C:\\Recycler\\explorer.exe  13");
    
    Sleep(1000);
    
    printf("[+] Disabled by renaming C:\\Recycler\\explorer.exe to 13 ...\n");
    printf("[+] Restart your computer ...\n");
    
    Sleep(1000);

    puts("[+] Backdoor.Win32.Agent.xs PWNED!");
    puts("[+] MD5: 6c51a5ba17ffd317ad08541e20131ef3");
    puts("[+] By Malvuln");
    system("pause");
  
}


C:\>cacls \Recycler
C:\Recycler 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


C:\>dir /a \Recycler
 Volume in drive C has no label.

 Directory of C:\Recycler

02/16/2021  04:19 PM    <DIR>          .
02/16/2021  04:19 PM    <DIR>          ..
02/16/2021  04:19 PM            77,824 explorer.exe
               1 File(s)         77,824 bytes
               2 Dir(s)  62,863,994,880 bytes free


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