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SoX buffer overflows when handling .WAV files
From: Ulf Härnhammar <Ulf.Harnhammar.9485 () student uu se>
Date: Wed, 28 Jul 2004 20:53:13 +0200

SoX buffer overflows when handling .WAV files


I have found two buffer overflows in SoX. They occur when the sox
or play commands handle malicious .WAV files. The overflows have
the identifier CAN-2004-0557.

Versions 12.17.4, 12.17.3 and 12.17.2 are vulnerable to these
overflows. Vulnerable versions of the program are included in many
Linux distributions and *BSD Port/Package Collections. Older versions
including 12.17.1, 12.17 and 12.16 are not vulnerable.

SoX may not be the most security critical program, but it is possible
to exploit this. Some attack vectors are social engineering (I have
used play to play .WAV files from untrusted sources several times
before I found this), programs that use SoX to play data from the net
(examples include JiveAudio and vmail), and people who put play in
their mailcap files (so it plays sound files in MIME messages as
soon as the messages are opened). It is also interesting to note
that xmms can play .WAV files with this type of data just fine.

Both overflows occur in wav.c in the function st_wavstartread().
In both cases, the program first reads 4 bytes from the .WAV file
into a variable. Then it reads as many bytes as that variable says
from the .WAV file into a 256 bytes long char array, without checking
if the data from the .WAV file fits in that array. This leads to a
stack-based buffer overflow with control over EIP, as you can see
in this session capture:


$ play buffy.wav
playing buffy.wav
/usr/bin/play: line 1:  4990 Segmentation fault      sox $volume
$fopts $fopts2 "$filename_0" $arch_defines $device $effects
$ sox buffy.wav -t ossdsp /dev/dsp
Segmentation fault
$ gdb /usr/bin/sox
GNU gdb 6.1-debian
Copyright 2004 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and
you are welcome to change it and/or distribute copies of it under
certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for
details.
This GDB was configured as "i386-linux"......Using host libthread_db
library "/lib/libthread_db.so.1".

(gdb) r buffy.wav -t ossdsp /dev/dsp
Starting program: /usr/bin/sox buffy.wav -t ossdsp /dev/dsp
Program received signal SIGSEGV, Segmentation fault.
0x55555555 in ?? ()
(gdb) i r
eax            0x0      0
ecx            0x0      0
edx            0x0      0
ebx            0x55555555       1431655765
esp            0xbffff940       0xbffff940
ebp            0x55555555       0x55555555
esi            0x55555555       1431655765
edi            0x55555555       1431655765
eip            0x55555555       0x55555555
eflags         0x10282  66178
cs             0x23     35
ss             0x2b     43
ds             0x2b     43
es             0x2b     43
fs             0x0      0
gs             0x0      0
(gdb) bt
#0  0x55555555 in ?? ()
#1  0x55555555 in ?? ()
#2  0x55555555 in ?? ()
#3  0x55555555 in ?? ()
#4  0x55555555 in ?? ()
#5  0x55555555 in ?? ()
#6  0x55555555 in ?? ()
#7  0xbffff900 in ?? ()
#8  0x08072fa2 in _IO_stdin_used ()
#9  0x00008572 in ?? ()
#10 0x45564157 in ?? ()
#11 0x002a5550 in ?? ()
#12 0x0807d0b8 in ?? ()
#13 0x0807d3c4 in ?? ()
#14 0x080a4400 in ?? ()
#15 0xbffff9a8 in ?? ()
#16 0x0804c9b7 in ?? ()
#17 0x08072f56 in _IO_stdin_used ()
#18 0xbffffb74 in ?? ()
#19 0x00000000 in ?? ()
#20 0x00000000 in ?? ()
#21 0x080a4400 in ?? ()
#22 0x00000005 in ?? ()
#23 0xbffff9c8 in ?? ()
#24 0x0804ad4b in ?? ()
#25 0x080a3cd8 in ?? ()
#26 0x00000001 in ?? ()
#27 0xbffff9c8 in ?? ()
#28 0x0804a42b in ?? ()
#29 0x080a4400 in ?? ()
#30 0x000005b4 in ?? ()
#31 0x76000001 in ?? ()
#32 0x00000005 in ?? ()
#33 0x080a4400 in ?? ()
#34 0x00000005 in ?? ()
#35 0xbffff9f8 in ?? ()
#36 0x0804a08b in ?? ()
#37 0x080a4400 in ?? ()
#38 0x00000005 in ?? ()
#39 0xbffffa54 in ?? ()
#40 0x080725bb in ?? ()
#41 0x402a5550 in ?? () from /lib/libc.so.6
#42 0x08072600 in ?? ()
#43 0x00000001 in ?? ()
#44 0x402a5550 in ?? () from /lib/libc.so.6
#45 0x400164a0 in ?? () from /lib/ld-linux.so.2
#46 0xbffffa54 in ?? ()
#47 0xbffffa28 in ?? ()
#48 0x4018bdc6 in __libc_start_main () from /lib/libc.so.6
Previous frame inner to this frame (corrupt stack?)
(gdb) q
The program is running.  Exit anyway? (y or n) y
$


I have attached a .WAV file that causes a buffer overflow, as well
as a patch against 12.17.4 that stops both overflows.

I contacted upstream, the vendor-sec list and naddy (an
OpenBSD/FreeBSD guy) on the 18th of July. I received the CAN/CVE
identifier on the same day. The 28th was agreed upon as the release
date, so I am releasing this now.

Greetings to Sitic, Sanctum Inc, Secunia, OWASP, Gobbles, F-Secure,
Ladytron, Vic Twenty (the band), Naked Ape, Slagsmalsklubben and
everyone from the Debian Security Audit Project.


// Ulf Harnhammar
   [ http://www.advogato.org/person/metaur/ ]
   for the Debian Security Audit Project
   [ http://www.debian.org/security/audit/ ]

Attachment: buffy.wav
Description:

Attachment: sox.patch
Description:


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