############################## Luigi Auriemma Application: VideoLAN (VLC) http://www.videolan.org Versions: <= 0.8.6d (the bug in ParseSSA affects version 0.8.6e too) Platforms: Windows, Mac, *BSD, *nix and more Bugs: A] buffer-overflow in the handling of the subtitles (originally found by Michal Luczaj) B] format string in the web interface Exploitation: A] local B] remote Date: 24 Dec 2007 Author: Luigi Auriemma e-mail: aluigi@autistici.org web: aluigi.org ####################################################################### 1) Introduction 2) Bugs 3) The Code 4) Fix ################################## =============== 1) Introduction =============== VideoLAN (VLC) is one of the most famous and used media players for various reasons: simple to use, open source, multi platform, many features available, continuosly updated and more. ################################# ======= 2) Bugs ======= --------------------------------------------------- A] buffer-overflow in the handling of the subtitles --------------------------------------------------- VLC is able to handle the subtitles automatically in a very simple way, it just checks the presence of ssa files with the same name of the loaded video and a possible subtitles folder. The functions which handle the MicroDvd, SSA and Vplayer subtitle formats are vulnerable to some stack based buffer-overflow vulnerabilities which can allow an attacker to execute malicious code. from modules\demux\subtitle.c: static int ParseMicroDvd( demux_t *p_demux, subtitle_t *p_subtitle ) ... char buffer_text[MAX_LINE + 1]; ... if( sscanf( s, "{%d}{}%[^\r\n]", &i_start, buffer_text ) == 2 || sscanf( s, "{%d}{%d}%[^\r\n]", &i_start, &i_stop, buffer_text ) == 3) static int ParseSSA( demux_t *p_demux, subtitle_t *p_subtitle ) ... char buffer_text[ 10 * MAX_LINE]; char buffer_text2[ 10 * MAX_LINE]; ... if( sscanf( s, "Dialogue: %[^,],%d:%d:%d.%d,%d:%d:%d.%d,%[^\r\n]", buffer_text2, &h1, &m1, &s1, &c1, &h2, &m2, &s2, &c2, buffer_text ) == 10 ) UPDATE 16 Mar 2008 in version 0.8.6e we have the following "wrong" change which leaves buffer_text2 still vulnerable: "Dialogue: %[^,],%d:%d:%d.%d,%d:%d:%d.%d,%81920[^\r\n]" static int ParseVplayer( demux_t *p_demux, subtitle_t *p_subtitle ) ... char buffer_text[MAX_LINE + 1]; ... if( sscanf( p, "%d:%d:%d%[ :]%[^\r\n]", &h, &m, &s, &c, buffer_text ) == 5 ) As written in the header of this advisory, these buffer-overflow bugs have been originally found and reported by Michal Luczaj this summer and the strange thing is that the SVN is fixed from that time BUT the current 0.8.6d (both executables and source code!) is still vulnerable. References: http://mailman.videolan.org/pipermail/vlc-devel/2007-June/032672.html http://mailman.videolan.org/pipermail/vlc-devel/2007-June/033394.html http://trac.videolan.org/vlc/browser/trunk/modules/demux/subtitle.c?rev=20715 ------------------------------------- B] format string in the web interface ------------------------------------- VLC can be controlled remotely through a nice web interface (a mini http server which must be manually activated) that runs by default on port 8080. The instructions which handle the Connection parameter sent by the client pass its content to the httpd_MsgAdd function without the needed format argument. In addition the new formatted Connection field is also sent back by the server in its reply, very useful for the attacker to tune the own exploit for increasing the percentage of success of the attack. from network\httpd.c: static int httpd_FileCallBack( httpd_callback_sys_t *p_sys, httpd_client_t *cl, httpd_message_t *answer, httpd_message_t *query ) ... psz_connection = httpd_MsgGet( &cl->query, "Connection" ); if( psz_connection != NULL ) { httpd_MsgAdd( answer, "Connection", psz_connection ); } ############################## =========== 3) The Code =========== http://aluigi.org/poc/vlcboffs.zip A] open vlcbof.avi and the ssa subtitle will be loaded automatically B] nc SERVER 8080 -v -v < vlcfs.txt ################################ ====== 4) Fix ====== Current SVN is fixed. The nightly builds are available here: http://nightlies.videolan.org ################