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Date: Sun, 21 Feb 2021 00:36:51 -0500
From: malvuln <malvuln13@...il.com>
To: fulldisclosure@...lists.org
Subject: [FD] Backdoor.Win32.DarkKomet.irv / Insecure Permissions

Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source:
https://malvuln.com/advisory/a229acff4e0605ad24eaf3d9c44fdb1b.txt
Contact: malvuln13@...il.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.DarkKomet.irv
Vulnerability: Insecure Permissions
Description: DarkKomet.irv creates an insecure dir named "Windupdt" under
c:\ drive, granting change (C) permissions to authenticated user group.
Standard users can rename the malware and reboot to disable it or replace
it with their own executable to escalate privileges when a privileged user
logs on. DarkKomet also creates auto start registry keys under
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run and
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
"Userinit" and drops three other files under "AppData\Local\Temp". To
successfully rename the malware we have to call Windows "attrib -h" command
to unhide the executable or the rename will fail.

Type: PE32
MD5: a229acff4e0605ad24eaf3d9c44fdb1b
Vuln ID: MVID-2021-0105
Dropped files: winupdate.exe, [TGS]CAPUB V1.11.EXE, [TGS]CAPUB V1.11.DLL,
dclogs.sys
Disclosure: 02/21/2021


Exploit/PoC:
#include "stdio.h"
#include "windows.h"

void main(void){

    system("attrib -h C:\\Windupdt\\winupdate.exe");
    puts("Unhiding the malware to rename it...");
    system("RENAME C:\\Windupdt\\winupdate.exe  13");

    Sleep(1000);
    printf("[+] Disabled persistence by renaming winupdate.exe to 13
...\n");
    printf("Restart your computer ...");

    puts("[+] Backdoor.Win32.DarkKomet.irv PWNED!\n");
    puts("[+] MD5: a229acff4e0605ad24eaf3d9c44fdb1b\n");
    puts("[+] By Malvuln\n");
    system("pause");

}

C:\Windupdt 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 \Windupdt
 Volume in drive C has no label.

 Directory of C:\Windupdt

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

 Directory of C:\Windupdt

06/14/2012  10:58 PM         1,433,088 winupdate.exe
               1 File(s)      1,537,340 bytes
               2 Dir(s)  49,992,314,880 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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