Discovery / credits: Malvuln - (c) 2021  
Original source:  
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   
void main(void){  
puts("[+] Unhiding the malware to rename it...");  
system("attrib -h C:\\Recycler\\explorer.exe");  
system("RENAME C:\\Recycler\\explorer.exe 13");  
printf("[+] Disabled by renaming C:\\Recycler\\explorer.exe to 13 ...\n");  
printf("[+] Restart your computer ...\n");  
puts("[+] Backdoor.Win32.Agent.xs PWNED!");  
puts("[+] MD5: 6c51a5ba17ffd317ad08541e20131ef3");  
puts("[+] By Malvuln");  
C:\>cacls \Recycler  
C:\Recycler BUILTIN\Administrators:(OI)(CI)(ID)F  
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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