CERT Advisory - Apache Web Server Chunk Handling Vulnerability (CA-2002-17)

CERT Advisory CA-2002-17 Apache Web Server Chunk Handling Vulnerability 

   Original release date: June 17, 2002 
   Last revised: -- 
   Source: CERT/CC 

   A complete revision history can be found at the end of this file. 

Systems Affected 

     * Web servers based on Apache code versions 1.3 through 1.3.24 
     * Web servers based on Apache code versions 2.0 through 2.0.36 


   There is a remotely exploitable vulnerability in the handling of large 
   chunks of data in web servers that are based on Apache source code. 
   This vulnerability is present by default in configurations of Apache 
   web servers versions 1.3 through 1.3.24 and versions 2.0 through 
   2.0.36. The impact of this vulnerability is dependent upon the 
   software version and the hardware platform the server is running on. 

I. Description 

   Apache is a popular web server that includes support for chunk-encoded 
   data according to the HTTP 1.1 standard as described in RFC2616. There 
   is a vulnerability in the handling of certain chunk-encoded HTTP 
   requests that may allow remote attackers to execute arbitrary code. 

   The Apache Software Foundation has published an advisory describing 
   the details of this vulnerability. This advisory is available on their 
   web site at 


II. Impact 

   For Apache versions 1.3 through 1.3.24 inclusive, this vulnerability 
   may allow the execution of arbitrary code by remote attackers. Several 
   sources have reported that this vulnerability can be used by intruders 
   to execute arbitrary code on Windows platforms. Additionally, the 
   Apache Software Foundation has reported that a similar attack may 
   allow the execution of arbitrary code on 64-bit UNIX systems. 

   For Apache versions 2.0 through 2.0.36 inclusive, the condition 
   causing the vulnerability is correctly detected and causes the child 
   process to exit. Depending on a variety of factors, including the 
   threading model supported by the vulnerable system, this may lead to a 
   denial-of-service attack against the Apache web server. 

III. Solution 

Apply a patch from your vendor 

   Apply a patch from your vendor to correct this vulnerability. The 
   CERT/CC has been informed by the Apache Software Foundation that the 
   patch provided in the ISS advisory on this topic does not completely 
   correct this vulnerability. More information about vendor-specific 
   patches can be found in the vendor section of this document. Because 
   the publication of this advisory was unexpectedly accelerated, 
   statements from all of the affected vendors were not available at 
   publication time. As additional information from vendors becomes 
   available, this document will be updated. 

Upgrade to the latest version 

   The Apache Software Foundation has released two new versions of Apache 
   that correct this vulnerability. System administrators can prevent the 
   vulnerability from being exploited by upgrading to Apache version 
   1.3.25 or 2.0.39. The new versions of Apache will be available from 
   their web site at 


Appendix A. - Vendor Information 

   This appendix contains information provided by vendors for this 
   advisory. As vendors report new information to the CERT/CC, we will 
   update this section and note the changes in our revision history. If a 
   particular vendor is not listed below, we have not received their 

Apache Software Foundation 

   New versions of the Apache software are available from: 


Conectiva Linux 

   The Apache webserver shipped with Conectiva Linux is vulnerable to 
   this problem. New packages fixing this problem will be announced to 
   our mailing list after an official fix becomes available. 

Cray, Inc. 

   Cray, Inc. does not distribute Apache with any of its operating 

IBM Corporation 

   IBM makes the Apache Server availble for AIX customers as a software 
   package under the AIX-Linux Affinity initiative. This package is 
   included on the AIX Toolbox for Linux Applications CD, and can be 
   downloaded via the IBM Linux Affinity website. The currently available 
   version of Apache Server is susceptible to the vulnerability described 
   here. We will update our Apache Server offering shortly to version 
   1.3.23, including the patch for this vulnerability; this update will 
   be made available for downloading by accessing this URL: 


   and following the instructions presented there. 

   Please note that Apache Server, and all Linux Affinity software, is 
   offered on an "as-is" basis. IBM does not own the source code for this 
   software, nor has it developed and fully tested this code. IBM does 
   not support these software packages. 


   We have verified that the Lotus Domino web server is not vulnerable to 
   this type of problem. Also, we do not ship Apache code with any Lotus 

Microsoft Corporation 

   Microsoft does not ship the Apache web server. 

Network Appliance 

   NetApp systems are not vulnerable to this problem. 

RedHat Inc. 

   Red Hat distributes Apache 1.3 versions in all Red Hat Linux 
   distributions, and as part of Stronghold. However we do not distribute 
   Apache for Windows. We are currently investigating the issue and will 
   work on producing errata packages when an official fix for the problem 
   is made available. When these updates are complete they will be 
   available from the URL below. At the same time users of the Red Hat 
   Network will be able to update their systems using the 'up2date' tool. 


Unisphere Networks 

   The Unisphere Networks SDX-300 Service Deployment System (aka. SSC) 
   uses Apache 1.3.24. We are releasing Version 3.0 using Apache 1.3.25 
   soon, and will be issuing a patch release for SSC Version 2.0.3 in the 
   very near future. 

   The CERT/CC thanks Mark Litchfield for reporting this vulnerability to 
   the Apache Software Foundation, and Mark Cox for reporting this 
   vulnerability to the CERT/CC. 

   Author: Cory F. Cohen 

   This document is available from: 

CERT/CC Contact Information 

   Email: cert@cert.org 
          Phone: +1 412-268-7090 (24-hour hotline) 
          Fax: +1 412-268-6989 
          Postal address: 
          CERT Coordination Center 
          Software Engineering Institute 
          Carnegie Mellon University 
          Pittsburgh PA 15213-3890 

   CERT/CC personnel answer the hotline 08:00-17:00 EST(GMT-5) / 
   EDT(GMT-4) Monday through Friday; they are on call for emergencies 
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   Any material furnished by Carnegie Mellon University and the Software 
   Engineering Institute is furnished on an "as is" basis. Carnegie 
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   Conditions for use, disclaimers, and sponsorship information 

   Copyright 2002 Carnegie Mellon University. 

   Revision History 
June 17, 2002: Initial release 

Version: PGP 6.5.8 



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