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Advisory: VLC media player TiVo ty Processing Stack Overflow
Vulnerability
Advisory ID: TKADV2008-010
Revision: 1.0
Release Date: 2008/10/20
Last Modified: 2008/10/20
Date Reported: 2008/10/18
Author: Tobias Klein (tk at trapkit.de)
Affected Software: VLC media player <= 0.9.4
Remotely Exploitable: Yes
Locally Exploitable: No
Vendor URL: http://www.videolan.org/
Vendor Status: Vendor has released an updated version
Patch development time: 1 day

======================
Vulnerability details:

The VLC media player contains a stack overflow vulnerability while parsing
malformed TiVo ty media files. The vulnerability can be trivially exploited
by a (remote) attacker to execute arbitrary code in the context of VLC
media player.

==================
Technical Details:

Source code file: modules\demux\Ty.c

[…]
1623 static void parse_master(demux_t *p_demux)
1624 {
1625 demux_sys_t p_sys = p_demux->p_sys;
1626 uint8_t mst_buf[32]; <– [1]
1627 int i, i_map_size;
1628 int64_t i_save_pos = stream_Tell(p_demux->s);
1629 int64_t i_pts_secs;
1630
1631 / Note that the entries in the SEQ table in the stream may have
1632 different sizes depending on the bits per entry. We store them
1633 all in the same size structure, so we have to parse them out one
1634 by one. If we had a dynamic structure, we could simply read the
1635 entire table directly from the stream into memory in place. /
1636
1637 / clear the SEQ table /
1638 free(p_sys->seq_table);
1639
1640 / parse header info /
1641 stream_Read(p_demux->s, mst_buf, 32); <– [2]
1642 i_map_size = U32_AT(&mst_buf[20]); <– [3]
1643 p_sys->i_bits_per_seq_entry = i_map_size * 8;
1644 i = U32_AT(&mst_buf[28]); / size of SEQ table, in bytes /
1645 p_sys->i_seq_table_size = i / (8 + i_map_size);
1646
1647 / parse all the entries */
1648 p_sys->seq_table = malloc(p_sys->i_seq_table_size *
sizeof(ty_seq_table_t));
1649 for (i=0; i<p_sys->i_seq_table_size; i++) {
1650 stream_Read(p_demux->s, mst_buf, 8 + i_map_size); <– [4]
[…]

[1] This stack buffer can be overflowed
[2] 32 bytes of user controlled file data are copied into "mst_buf"
[3] "i_map_size" is extracted from the user controlled file data
[4] The user controlled value of "i_map_size" is used as a length value
for the "stream_Read()" function. This function copies "i_map_size"
bytes of file data (that can also be controlled by the attacker) into
the stack buffer "mst_buf". This leads to a straight stack overflow
that can be trivially exploited by a (remote) attacker to execute
arbitrary code in the context of VLC.

=========
Solution:

See "Workarounds" and "Solution" sections of the VideoLAN-SA-0809 [1].

========
History:

2008/10/18 - Vendor notified
2008/10/18 - Patch developed
2008/10/20 - Public disclosure of vulnerability details by the vendor
2008/10/20 - Release date of this security advisory

========
Credits:

Vulnerability found and advisory written by Tobias Klein.

===========
References:

[1] http://www.videolan.org/security/sa0809.html
[2] http://git.videolan.org/?p=vlc.git;a=commitdiff;h=26d92b87bba99b5ea2
e17b7eaa39c462d65e9133
[3] http://www.trapkit.de/advisories/TKADV2008-010.txt

========
Changes:

Revision 0.1 - Initial draft release to the vendor
Revision 1.0 - Public release

===========
Disclaimer:

The information within this advisory may change without notice. Use
of this information constitutes acceptance for use in an AS IS
condition. There are no warranties, implied or express, with regard
to this information. In no event shall the author be liable for any
direct or indirect damages whatsoever arising out of or in connection
with the use or spread of this information. Any use of this
information is at the user's own risk.

==================
PGP Signature Key:

http://www.trapkit.de/advisories/tk-advisories-signature-key.asc

Copyright 2008 Tobias Klein. All rights reserved.

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