Dear Benjamin Tober,

Latest release mpg123 0.59r uses large enough buffer size and may not be
exploited this way. But both versions have another one bug in frame size
calculation - zero bitrate will lead to negative frame size to be
calculated. Unchecked patches:

for 0.59r:

--- common.old 2003-01-15 21:42:15.000000000 +0300
+++ common.c 2003-01-15 21:42:38.000000000 +0300
@@ -123,7 +123,7 @@
return FALSE;
if(!((head>>17)&3))
return FALSE;
- if( ((head>>12)&0xf) == 0xf)
+ if( ((head>>12)&0xf) == 0xf || (head>>12)&0xf) == 0)
return FALSE;
if( ((head>>10)&0x3) == 0x3 )
return FALSE;

for pre0.59s:

--- common.old 2003-01-15 20:51:15.000000000 +0300
+++ common.c 2003-01-15 20:25:26.000000000 +0300
@@ -127,7 +127,7 @@
return FALSE;
if(!((head>>17)&3))
return FALSE;
- if( ((head>>12)&0xf) == 0xf || (head>>12)&0xf) == 0)
+ if( ((head>>12)&0xf) == 0xf)
return FALSE;
if( ((head>>10)&0x3) == 0x3 )
return FALSE;
@@ -140,7 +140,7 @@
* -1: giving up
* 1: synched
*/
-#define MAX_INPUT_FRAMESIZE 1920
+#define MAX_INPUT_FRAMESIZE 4096
#define SYNC_HEAD_MASK 0xffff0000
#define SYNC_HEAD_MASK_FF 0x0000f000
#define LOOK_AHEAD_NUM 3
@@ -237,6 +237,8 @@
}
}
else {
+ if(frameInfo.framesize > MAX_INPUT_FRAMESIZE) return 0;
+
if(!rds->read_frame_body(rds,dummybuf,frameInfo.framesize))
return 0;

--Wednesday, January 15, 2003, 11:16:24 AM, you wrote to bugtraq (at) securityfocus (dot) com [email concealed]:

BT> In-Reply-To: <200301131823.h0DINJbE014752 (at) mailserver3.hushmail (dot) com [email concealed]>

BT> I'm not going to address the veracity of the narrative
BT> text of this posting, however the exploit is real. I
BT> believe that the patch to mpg123 given below closes
BT> this particular hole. I have no affiliation with the
BT> authors of mpg123 and haven't contacted them, but am
BT> providing this patch now because an exploit is
BT> publically available.
BT> I can, if necessary, provide further explanation of the
BT> exploit and the rationale behind the patch but will not
BT> do so at this late hour. This patch is with respect to
BT> mpg123-pre0.59s and is to the file common.c:

BT> --- common.c.orig Wed Jan 15 02:16:08 2003
BT> +++ common.c Wed Jan 15 02:18:52 2003
BT> @@ -579,6 +579,11 @@
BT> fprintf(stderr,"Sorry, unknown layer
BT> type.\n");
BT> return (0);
BT> }
BT> + if (fr->framesize>MAX_INPUT_FRAMESIZE) {
BT> + fprintf(stderr,"Frame size too big.\n");
BT> + fr->framesize = MAX_INPUT_FRAMESIZE;
BT> + return 0;
BT> + }

BT> if(!fr->bitrate_index) {
BT> /* fprintf(stderr,"Warning, Free format not
BT> heavily tested: (head %08lx)\n",newhead); */

BT> Sincerely,
BT> Benjamin Tober

--
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