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             AUSCERT External Security Bulletin Redistribution

           ESB-2004.0788 -- iDEFENSE Security Advisory 12.16.04
         MPlayer Bitmap Parsing Remote Heap Overflow Vulnerability
                             17 December 2004

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        AusCERT Security Bulletin Summary
        ---------------------------------

Product:           MPlayer
Publisher:         iDEFENSE
Operating System:  UNIX variants
                   Linux variants
Impact:            Execute Arbitrary Code/Commands
Access:            Remote/Unauthenticated

Ref:               ESB-2004.0787
                   ESB-2004.0786

Original Bulletin: http://www.idefense.com/application/poi/display?id=168

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MPlayer Bitmap Parsing Remote Heap Overflow Vulnerability

iDEFENSE Security Advisory 12.16.04
http://www.idefense.com/application/poi/display?id=168
December 16, 2004

I. BACKGROUND

MPlayer is a movie player for Linux that also runs on many other Unices,

and non- x86 CPUs. It plays most MPEG, VOB, AVI, Ogg/OGM, VIVO, 
ASF/WMA/WMV, QT/MOV/MP4, FLI, RM, NuppelVideo, YUV4MPEG, FILM, RoQ, PVA 
files, supported by many native, XAnim, and Win32 DLL codecs. You can 
watch VideoCD, SVCD, DVD, 3ivx, DivX 3/4/5 and other formats. 

More information is available at http://mplayerhq.hu/.

II. DESCRIPTION

Remote exploitation of a heap overflow vulnerability in Unix MPlayer 
could allow attackers to gain access to the computer. 

The vulnerability specifically exists due to a lack of bounds checking 
within the demux_open_bmp() routine defined in /libmpdemux/demux_bmp.c. 
If a specially crafted file specifies a large value for the "biClrUsed" 
field, an overflow is triggered in stream_read(). 

The vulnerable portion of code is displayed here: 

demuxer_t* demux_open_bmp(demuxer_t* demuxer)
{
    sh_video_t *sh_video = NULL;
    unsigned int filesize;
    unsigned int data_offset;
    bmp_image_t *bmp_image;
    ...
    sh_video->bih->biClrUsed = stream_read_dword_le(demuxer->stream);
    sh_video->bih->biClrImportant =
stream_read_dword_le(demuxer->stream);
    // fetch the palette
[!]  stream_read(demuxer->stream, (unsigned char *)(sh_video->bih) + 40,
    sh_video->bih->biClrUsed * 4);
    ...
} 

In the given example call to stream_read(), an unchecked amount of data 
as specified by "biClrUsed" will be read into the fixed size buffer 
"bih." This allows control of execution by overwriting the saved return 
address on the stack.

III. ANALYSIS

Successful exploitation of this vulnerability allows remote attackers to

execute arbitrary code under the privileges of the user who attempted to

view the bitmap file. Exploitation is not trivial, as a high level of 
precision is required. It is not a requirement for the malicious file to

have an extension of .bmp because MPlayer will correctly determine if it

is a bitmap file despite its extension.

IV. DETECTION

iDEFENSE has confirmed that MPlayer version 1.0pre5 is vulnerable.

The following distributions of Linux include MPlayer:
	
	Debian Linux 
	Fedora Linux 
	Gentoo Linux 
	SUSE Linux 

V. WORKAROUND

Users must be careful when accepting and opening media from untrusted 
sources.

VI. VENDOR RESPONSE

A patch to address this vulnerability is available at:

http://www1.mplayerhq.hu/MPlayer/patches/bmp_fix_20041215.diff

VII. CVE INFORMATION

A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not
been assigned yet.

VIII. DISCLOSURE TIMELINE

12/10/2004  Initial vendor notification
12/16/2004  Public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

Get paid for vulnerability research
http://www.idefense.com/poi/teams/vcp.jsp

X. LEGAL NOTICES

Copyright (c) 2004 iDEFENSE, Inc.

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without the express
written consent of iDEFENSE. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically, please
email customerservice@idefense.com for permission.

Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
this information.



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