[NT] SecureW2 Weak Random Seeding for PMS

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  SecureW2 Weak Random Seeding for PMS
------------------------------------------------------------------------


SUMMARY

 <http://www.securew2.com/uk/> SecureW2 - "powerful open source EAP-TTLS 
Client for Windows."

SecureW2 uses weak random number seeding when it generates the PMS (Pre 
Master Secret).

DETAILS

Vulnerable Systems:
 * SecureW2 versions 3.0 and prior

SecureW2 uses weak random numbers when generating the pre-master-secret.

Vulnerable code:
The code quoted below can be found in 
"./Components/Common/release3/version 0/source/CommonTLS.c":
//
// Name: TLSGenPMS
// Description: Generate the 48 random bytes for the PMS (Pre Master 
Secret)
// Author: Tom Rixom
// Created: 17 December 2002
//
DWORD
TLSGenPMS( IN OUT BYTE pbPMS[TLS_PMS_SIZE] )
{
        int                             i = 0;
        SYSTEMTIME              SystemTime;
        DWORD                   dwRet;

        dwRet = NO_ERROR;

        AA_TRACE( ( TEXT( "TLSGenPMS" ) ) );

        pbPMS[0] = 0x03;
        pbPMS[1] = 0x01;

        //
        // Time (DWORD)
        //
        GetLocalTime( &SystemTime );

        srand( ( unsigned int ) SystemTime.wMilliseconds );

        //srand( ( unsigned )time( NULL ) );

        //
        // Random bytes
        //
        for( i=2; i < TLS_PMS_SIZE; i++ )
                pbPMS[i] = ( BYTE ) ( rand() % 255 );

        AA_TRACE( ( TEXT( "TLSGenPMS::random bytes: %s" ), AA_ByteToHex( 
pbPMS, TLS_PMS_SIZE ) ) );

        return dwRet;
}

It appear to be using the weak srand/rand functions seeded by the 
milliseconds field from the system clock.  That doesn't provide you with 
48 bytes of strong randomness, you are lucky to get even a few bytes.


ADDITIONAL INFORMATION

The information has been provided by  <mailto:jas@xxxxxxxxxxx> Simon 
Josefsson.



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