full-disclosure - [FD] Backdoor.Win32.Agent.xs / Insecure Permissions

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Message-ID: <CAAHK0WTjDQAUQ-xpWRf543qW58hYh14XJar+eSMhN_SZV03JOw@mail.gmail.com>
Date: Tue, 23 Feb 2021 20:24:52 -0500
From: malvuln <malvuln13@...il.com>
To: fulldisclosure@...lists.org
Subject: [FD] Backdoor.Win32.Agent.xs / Insecure Permissions

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

Disclaimer: The information contained within this advisory is supplied
"as-is" with no warranties or guarantees of fitness of use or otherwise.
Permission is hereby granted for the redistribution of this advisory,
provided that it is not altered except by reformatting it, and that due
credit is given. Permission is explicitly given for insertion in
vulnerability databases and similar, provided that due credit is given to
the author. The author is not responsible for any misuse of the information
contained herein and accepts no responsibility for any damage caused by the
use or misuse of this information. The author prohibits any malicious use
of security related information or exploits by the author or elsewhere. Do
not attempt to download Malware samples. The author of this website takes
no responsibility for any kind of damages occurring from improper Malware
handling or the downloading of ANY Malware mentioned on this website or
elsewhere. All content Copyright (c) Malvuln.com (TM).

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