#38322 [Opn->Csd]: reading past array in sscanf leads to arbitary code execution

From: Date: Fri, 04 Aug 2006 11:59:54 +0000
Subject: #38322 [Opn->Csd]: reading past array in sscanf leads to arbitary code execution
References: 1  Groups: php.bugs 
Request: Send a blank email to php-bugs+get-100331@lists.php.net to get a copy of this message 
 ID:               38322
 Updated by:       tony2001@php.net
 Reported By:      heintz at hotmail dot com
-Status:           Open
+Status:           Closed
 Bug Type:         Strings related
 Operating System: all
 PHP Version:      5.1.4
 New Comment:

This bug has been fixed in CVS.

Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.
 
Thank you for the report, and for helping us make PHP better.




Previous Comments:
------------------------------------------------------------------------

[2006-08-04 11:36:16] heintz at hotmail dot com

the checkformat function checks the invalid numbers
by subtracting one but the scanning function doesnt
so seems to me the only problem here is that someone has forgotten to
subract 1
code from scanf.c line 737

} else if ( isdigit(UCHAR(*ch))) { 
                value = strtoul(format-1, &end, 10); 
                if (*end == '$') {
                    format = end+1;
                    ch = format++;
                    objIndex = varStart + value;
                }
         }

i think just by putting making a objIndex = varStart + value -1;

it would be secure and keep the functionality. though the if-s wont
hurt if you subract one so they can stay for insurance if performance
is not that big of a issue.

------------------------------------------------------------------------

[2006-08-04 09:28:06] tony2001@php.net

Please check out this patch:
http://tony2001.phpclub.net/dev/tmp/bug38322.diff

------------------------------------------------------------------------

[2006-08-04 00:36:21] heintz at hotmail dot com

Description:
------------
ext/standard/scanf.c line ~887
  ---
  if (numVars) {
                    current = args[objIndex++];                
  ---
  
  objIndex points past the end of array in other format cases too





Reproduce code:
---------------
sscanf('foo ','$1s',$str);

http://www.plain-text.info/sscanf_bug.txt -
full description

Actual result:
--------------
will try to dereference a pointer to pointer which usually causes
segmentation fault


------------------------------------------------------------------------


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