[NEWS] zlib Buffer Overflow Vulnerability

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  zlib Buffer Overflow Vulnerability
------------------------------------------------------------------------


SUMMARY

 <http://www.zlib.net/> zlib is a compression and decompression library 
using the gzip format.

By creating a specially crafted compressed data stream, attackers can 
overwrite data structures for application that uses zlib. The result may 
cause the application to perform a denial of service by crashing, and may 
also allow attackers to execute arbitrary code.

DETAILS

Vulnerable Systems:
 * zlib version 1.2.1
 * zlib version 1.2.2

In order to exploit the vulnerability, attackers would have to create a 
special crafted compressed streamed data, that will trigger the buffer 
overflow with the inflate_table() function.
Vulnerable Code:
inftrees.c:

if (left > 0 && (type == CODES || (codes - count[0] != 1)))
  return -1;                      /* incomplete set */

Workaround:
You may apply an unofficial patch made by FreeBSD:

Index: lib/libz/inftrees.c
-=================================================================
RCS file: /home/ncvs/src/lib/libz/inftrees.c,v
retrieving revision 1.5
diff -u -p -r1.5 inftrees.c
--- lib/libz/inftrees.c 11 May 2005 03:47:48 -0000 1.5
+++ lib/libz/inftrees.c 2 Jul 2005 19:29:56 -0000
@@ -134,7 +134,7 @@ unsigned short FAR *work;
         left -= count[len];
         if (left < 0) return -1;        /* over-subscribed */
     }
-    if (left > 0 && (type == CODES || (codes - count[0] != 1)))
+    if (left > 0 && (type == CODES || max != 1))
         return -1;                      /* incomplete set */
 
     /* generate offsets into symbol table for each length for sorting */

CVE Information:
 <http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-2096> 
CAN-2005-2096


ADDITIONAL INFORMATION

The information has been provided by: Secunia  
<http://secunia.com/advisories/15949/> 
http://secunia.com/advisories/15949/ ,
FreeBSD Security  
<http://www.niscc.gov.uk/niscc/docs/br-20050707-00552.html?lang=en> 
http://www.niscc.gov.uk/niscc/docs/br-20050707-00552.html?lang=en ,
c-enter  <http://www.c-enter.hu/center/0250564.html> 
http://www.c-enter.hu/center/0250564.html,
Whitedust  <http://www.whitedust.net/speaks/837/> 
http://www.whitedust.net/speaks/837/



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