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: Wave audio
--- wav.c.old 2002-12-31 04:19:22.000000000 +0100
+++ wav.c 2004-07-18 19:25:46.000000000 +0200
@@ -917,6 +917,10 @@
} else if(strncmp(magic,"ICRD",4) == 0){
st_readdw(ft,&len);
len = (len + 1) & ~1;
+ if (len > 254) {
+ fprintf(stderr, "Possible buffer overflow hack
attack (ICRD)!\n");
+ exit(109);
+ }
st_reads(ft,text,len);
if (strlen(ft->comment) + strlen(text) < 254)
{
@@ -926,6 +930,10 @@
} else if(strncmp(magic,"ISFT",4) == 0){
st_readdw(ft,&len);
len = (len + 1) & ~1;
+ if (len > 254) {
+ fprintf(stderr, "Possible buffer overflow hack
attack (ISFT)!\n");
+ exit(110);
+ }
st_reads(ft,text,len);
if (strlen(ft->comment) + strlen(text) < 254)
{