Apache Web Server Chunk Handling Vulnerability
Last revised: November 2, 2007
A complete revision history can be found at the end of this file.
- Web servers based on Apache code versions 1.2.2 and above
- 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 way that Apache web servers (or other web servers based on their source code) handle data encoded in chunks. This vulnerability is present by default in configurations of Apache web server versions 1.2.2 and above, 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.
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
Vulnerability Note VU#944335 includes a list of vendors that have been contacted about this vulnerability.
For Apache versions 1.2.2 through 1.3.24 inclusive, this vulnerability may allow the execution of arbitrary code by remote attackers. Exploits are publicly available that claim to allow the execution of arbitrary code.
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.
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 httpd version 1.3.26 or 2.0.39.
Due to some unexpected problems with version 1.3.25, the CERT/CC has been informed by the Apache Software Foundation that the corrected version of the software is now 1.3.26. Both 1.3.26 and 2.0.39 are available on their web site at
Apply a patch from your vendor
If your vendor has provided a patch to correct this vulnerability, you may want to apply that patch rather than upgrading your version of httpd. The CERT/CC is aware of a patch from ISS that corrects some of the impacts associated with this vulnerability. System administrators are encouraged to ensure that the patch they apply is based on the code by the Apache Software Foundation that also corrects additional impacts described in this advisory.
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.
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 comments.
In relation to this CERT advisory on security vulnerability in Apache, Alcatel has conducted an immediate assessment to determine any impact this may have on our portfolio. A first analysis has shown that various Alcatel products can be affected: namely the A5000 and A5020 SoftSwitches, the A5735 SMC, the A1300 NMC2, the management platforms for the A1000 UMTS/GPRS/MSC solutions, the 1353 SH and 1355 VPN. Customers using these products should upgrade to Apache WebServer 1.3.26 (or higher) or may contact their Alcatel support representative for more details. The security of our customers' networks is of highest priority for Alcatel. Therefore we continue to test our product portfolio against potential security vulnerabilities in our products using the Apache Webserver and will provide updates if necessary.
Apache Software Foundation
New versions of the Apache software are available from:
Apple Computer, Inc.
This vulnerability is fixed with the release of the "Security Update - July 2002" software update.
Caldera has published several advisories describing this vulnerability:
Cisco Systems is evaluating the vulnerabilities identified by VU#944335. Should an issue be found, Cisco will release a Security Advisory. The most up-to-date information on all Cisco product security issues may be found at
Compaq Computer Corporation
Compaq has released Security Bulletin SSRT2253 (document number SRB0021W).
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.
Covalent Technologies distributes products based on Apache 1.3 and Apache 2.0 that may be subject to this vulnerability. Covalent is currently creating patches to affected products. Covalent customers will be informed by email, and by postings at www.covalent.net/support when the patches are available.
Cray, Inc. does not distribute Apache with any of its operating systems.
Guardian Digital ships Apache in all version of EnGarde Secure Linux. EnGarde Secure Profssional users may update using the GDSN. This issue was addressed in ESA-20020619-014 which may be found at:
The following F5 Networks, Inc. products contain a vulnerable version of the Apache-based web server. Instructions for obtaining and installing a patch are available in the following locations.
Fujitsu's UXP/V operating system does not support Apache and is therefore not affected by the vulnerability reported in VU#944335.
HP makes the Apache Server available for customers as a bundled software package called "HP Apache." New updates are available temporarily via ftp from a site located at hprc.external.hp.com.
When the new updates are available at www.software.hp.com, the Hewlett-Packard Company Security Bulletin HPSBUX0207-197 will be updated.
To retrieve the updates from the temporary ftp site, use a browser to connect to:
HP Virtualvault (HP-UX 11.04) patches are available from itrc.hp.com with ID's of PHSS_27361 and PHSS_27371.
For full details, see Hewlett-Packard Company Security Bulletin HPSBUX0207-197, available on itrc.hp.com. Search for "Apache chunk"
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.
The IBM HTTP Server product, which is also bundeled with the Websphere product,is based on the Apache server. As such, it is vulnerable to the current "Chunk Handling" issue and we are woring on a patch for this problem with all due haste. This statement will be updated as more information becomes available.
Information for the Websphere patches is available from the web. Go to this URL:
Click on the "Websphere Flashes" link and look for the item for "IBM HTTP Server". This will contain information on the exposure and links to the patches.
The IBM HMC product is also affected by the Apache vulnerability described above. The HMC is the hardware monitor and control console used with IBM's Regatta systems. This is a seperate hardware unit that uses a Linux-based operating system and Open Source software.
Customers are advised to obtain the latest security paches for the HMC. These patches will be available early next week from the following URL:
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 products.
Microsoft does not ship the Apache web server.
Data ONTAP(R) and NetCache(R) products are not affected.
ReplicatorX versions 4.0 through 4.0.21 are affected (This was originally released by Topio Inc, now a wholly owned subsidiary of NetApp, as Topio Data Protection Suite (TDPS) releases 1.0 through 3.0.65).
Contact the NetApp Technical Support Center +1-888-4NETAPP for remediation information and instructions.
Nortel Networks is reviewing its portfolio to determine if any products are affected by the vulnerability noted in CERT Advisory CA-2002-17. A definitive statement will be issued shortly.
Oracle has issued Oracle Security Alert #36 in response to the chunked encoding Apache HTTP Server security vulnerability.
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.
Secure Computing Corporation
In response to the CERT Advisory CA-2002-17, Secure Computing has posted a software patch for users of the SafeWord PremierAccess version 3.1 authentication system. All existing and new customers are advised to download and apply PremierAccess Patch 1. Patch 1(v3.1.0.01) is available for immediate web download at
SGI has released SGI Security Advisory 20020605-01-I.
Sun Microsystems Inc.
Sun bundles the Apache Web Server freeware product with Solaris 8 (Apache/1.3.12) and 9 (Apache/1.3.22). Both versions are affected by this vulnerability. Sun are presently producing patches for this issue for Solaris 8 and 9. Once the patches are available, we will be publishing a Sun Alert available from:
Unisphere NetworksCUSTOMER SERVICE TECHNICAL BULLETIN
SUBJECT: CERT Advisory CA-2002-17: Apache Web Server Chunk Handling Vulnerability
BULLETIN NUMBER: SSC_PSN-001
BULLETIN TYPE: Product Support Notification
AFFECTED PRODUCTS: SSC
ISSUE DATE: 06/26/2002
The CERT Coordination Center released an advisory on June 17, 2002 entitled, "CERT Advisory CA-2002-17 Apache Web Server Chunk Handling Vulnerability". The URL for the full text of the advisory can be found at:
The following releases of software have been found to suffer no negative effects from vulnerability outlined in CERT Advisory CA-2002-17:
2-0-2p2All future releases of SSC will include the updated version of Apache web server that corrects this vulnerability.
Earlier releases of software may allow the execution of arbitrary code by remote attackers. Information needed to exploit this vulnerability is publicly known.
Affected releases include:
2-0-0 -- 2-0-2p1This Product Support Notification is publicly viewable on the Web at:
2-0-3 -- 2-0-3p1
Inside the U.S. call: (800) 424-2344
Outside the U.S. call: (978) 589-9000
Via the Web @ http://support.unispherenetworks.com
Via email @ email@example.com
Trustix Secure Linux
Trustix Secure Linux has published an advisory on this topic:
A response to this advisory is available from our web site:
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
Copyright 2002 Carnegie Mellon University.
June 17, 2002: Initial release June 18, 2002: Added Fujitsu vendor statement. June 18, 2002: Added information about Apache version 1.2.2 and above. June 18, 2002: Added pointers to Apache versions including 1.3.26. June 19, 2002: Added Covalent vendor statement. June 19, 2002: Added Compaq vendor statement. June 19, 2002: Added Engarde vendor statement. June 19, 2002: Added SGI vendor statement. June 19, 2002: Updated Solution section to clarify patch capabilities. June 19, 2002: Added statement about exploit code for 32-bit platforms. June 19, 2002: Try to be as clear as possible on the impact (all systems). June 20, 2002: Added a link to the vulnerability note. June 20, 2002: Added Hewlett-Packard vendor statement. June 21, 2002: Added Oracle vendor statement. June 24, 2002: Added F5 Networks vendor statement. June 24, 2002: Updated IBM vendor statement to include Websphere information. June 24, 2002: Added Sun Microsystems Inc. vendor statement. June 27, 2002: Added Nortel vendor statement. June 27, 2002: Updated Unisphere vendor statement. June 28, 2002: Added Alcatel vendor statement. June 28, 2002: Added Apple vendor statement. July 08, 2002: Added Cisco vendor statement. July 15, 2002: Updated Hewlett-Packard vendor statement. July 15, 2002: Updated SGI vendor statement. July 15, 2002: Added Caldera vendor statement. July 15, 2002: Added Trustix vendor statement. July 16, 2002: Updated Compaq vendor statement. August 8, 2002: Added Xerox vendor statement. August 8, 2002: Updated IBM vendor statement. September 25, 2002: Added Secure Computing vendor statement. March 27, 2003: Updated Xerox vendor statement. November 2, 2007: Updated Network Appliance vendor statement.