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CERT Advisory CA-2002-07 Double Free Bug in zlib Compression Library

   Original release date: March 12, 2002
   Last revised: --
   Source: CERT/CC

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

Systems Affected

     * Any software that is linked to zlib 1.1.3 or earlier may be
       affected
     * Data compression libraries derived from zlib 1.1.3 or earlier may
       contain a similar bug

Overview

   There is a bug in the zlib compression library that may manifest
   itself as a vulnerability in programs that are linked with zlib. This
   may allow an attacker to conduct a denial-of-service attack, gather
   information, or execute arbitrary code.

   It is important to note that the CERT/CC has not received any reports
   of exploitation of this bug. Based on the information available to us
   at this time, it is difficult to determine whether this bug can be
   successfully exploited. However, given the widespread deployment of
   zlib, we have published this document as a proactive measure.

I. Description

   There is a bug in the decompression algorithm used by the popular zlib
   compression library. If an attacker is able to pass a
   specially-crafted block of invalid compressed data to a program that
   includes zlib, the program's attempt to decompress the crafted data
   can cause the zlib routines to corrupt the internal data structures
   maintained by malloc.

   The bug results from a programming error that causes segments of
   dynamically allocated memory to be released more than once (i.e.,
   "double-freed"). Specifically, when inftrees.c:huft_build() encounters
   the crafted data, it returns an unexpected Z_MEM_ERROR to
   inftrees.c:inflate_trees_dynamic(). When a subsequent call is made to
   infblock.c:inflate_blocks(), the inflate_blocks function tries to free
   an internal data structure a second time.

   Because this bug interferes with the proper allocation and
   deallocation of dynamic memory, it may be possible for an attacker to
   influence the operation of programs that include zlib. In most
   circumstances, this influence will be limited to denial of service or
   information leakage, but it is theoretically possible for an attacker
   to insert arbitrary code into a running program. This code would be
   executed with the permissions of the vulnerable program.

   The CERT/CC is tracking this issue as VU#368819. This reference number
   corresponds to CVE candidate CAN-2002-0059.

II. Impact

   This bug may introduce vulnerabilities into any program that includes
   the affected library. Depending upon how and where the zlib routines
   are called from the given program, the resulting vulnerability may
   have one or more of the following impacts: denial of service,
   information leakage, or execution of arbitrary code.

III. Solution

Upgrade your version of zlib

   The maintainers of zlib have released version 1.1.4 to address this
   vulnerability. Upgrade any software that is linked to or derived from
   an earlier version of zlib. The latest version of zlib is available at
   http://www.zlib.org

   These are the MD5 checksums for zlib version 1.1.4:

     abc405d0bdd3ee22782d7aa20e440f08 zlib-1.1.4.tar.gz
     9bf1d36ced334b0cf1f996f5c8171018 zlib114.zip

Apply a patch from your vendor

   The zlib compression library is freely available and used by many
   vendors in a wide variety of applications. Any one of these
   applications may contain vulnerabilities that are introduced by this
   vulnerability.

   Appendix A 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.
   Please contact your vendor directly.

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.

Apple Computer, Inc.

   Mac OS X and Mac OS X Server do not contain this vulnerability.

Compaq Computer Corporation

   COMPAQ COMPUTER CORPORATION
   -----------------------------
   x-ref: SSRT0818 zlib

   At the time of writing this document, Compaq continues to evaluate
   this potential problem and impacts to Compaq released software. Compaq
   will implement solutions based on the conclusion of this evaluation as
   necessary. Compaq will provide notice of any new patches as a result
   any required solution through standard patch notification procedures
   and be available from your normal Compaq Services support channel.
   COMPAQ COMPUTER CORPORATION
   -----------------------------

Conectiva Linux

   Conectiva Linux supported versions (5.0, 5.1, 6.0, 7.0, ferramentas
   graficas and ecomerce) are affected by the zlib vulnerability. Updates
   will be sent to our security mailing lists and be available at our ftp
   site and mirrors. The updates will include a new version of zlib
   itself and also other packages which include their own version of zlib
   or are linked statically to the system-wide copy of zlib.

Engarde

   EnGarde Secure Linux Community and Professional are both vulnerable to
   the zlib bugs. Guardian Digital addressed this vulnerability in
   ESA-20020311-008 which may be found at:

     http://www.linuxsecurity.com/advisories/other_advisory-1960.html

   EnGarde Secure Professional users may upgrade their systems using the
   Guardian Digital Secure Network.

FreeBSD

   FreeBSD is not vulnerable, as the FreeBSD malloc implementation
   detects and complains about several programming errors including this
   kind of double free.

Fujitsu

   Fujitsu's UXP/V operating system is not affected by the zlib
   vulnerability because it does not support zlib.

Hewlett-Packard Company

   HP is not vulnerable.

IBM Corporation

   IBM's AIX operating system, version 5.1, ships with open
   source-originated zlib that is used with the Redhat Package Manager
   (rpm) to install applications that are included in the AIX-Linux
   Affinity Toolkit. zlib (libz.a) is a shared library in AIX. AIX 5.1 is
   susceptible to the described vulnerability. AIX 4.3.x does not ship
   with zlib, but customers who install zlib and use it will be similarly
   vulnerable. IBM will make the patched version of zlib available as
   soon as it is made available to us.

OpenBSD

   OpenBSD is not vulnerable as OpenBSD's malloc implementation detects
   double freeing of memory. The zlib shipped with OpenBSD has been fixed
   in OpenBSD-current in January 2002.

Openwall GNU/*/Linux

   All versions of Openwall GNU/*/Linux (Owl) prior to the 2002/02/15
   Owl-current snapshot are affected by the zlib double-free
   vulnerability. Owl-current after 2002/02/15 includes the proper fixes
   in its userland packages. In order to not place the users of other
   vendors' products at additional risk, we have agreed to delay
   documenting this as a security change and including the fixes in Owl
   0.1-stable until there's a coordinated public announcement. While we
   don't normally support this kind of a policy (releasing a fix before
   there's an announcement), this time handling the vulnerability in this
   way was consistent with the state of things by the time the (already
   publicly known) bug was first realized to be a security vulnerability.

   The zlib bug could affect the following Owl packages: gnupg, openssh,
   rpm, texinfo (not necessarily in a security sense). Of these, the
   OpenSSH could potentially allow for an active remote attack resulting
   in a root compromise. If only SSH protocol version 1 is allowed in the
   OpenSSH server this is reduced to a local attack, but reverse remote
   attack possibilities by a malicious server remain. Additionally, any
   third-party software that makes use of the provided zlib library could
   be affected.

   Parts of the Linux 2.2 kernel included in Owl were also affected by
   the vulnerability. Fortunately, those parts (Deflate compression
   support for PPP and the experimental Deflate compression extension to
   IrDA) are normally not used by the Owl userland. The bug has been
   corrected starting with Linux 2.2.20-ow2 which has been made public
   and a part of both Owl-current and Owl 0.1-stable on 2002/03/03. This
   change, however, will only be documented in the publicly-available
   change logs on the coordinated public announcement date.

Red Hat, Inc.

   Red Hat Linux ships with a zlib library that is vulnerable to this
   issue. Although most packages in Red Hat Linux use the shared zlib
   library we have identified a number of packages that either statically
   link to zlib or contain an internal version of the zlib code.

   Updates to zlib and these packages as well as our advisory note are
   available from the following URL. Users of the Red Hat Network can use
   the up2date tool to automatically upgrade their systems.

     http://www.redhat.com/support/errata/RHSA-2002-026.html

   Red Hat would like to thank CERT/CC for their help in coordinating
   this issue with other vendors.

SGI

   SGI acknowledges the zlib vulnerabilities reported by CERT and is
   currently investigating. No further information is available at this
   time.

   For the protection of all our customers, SGI does not disclose,
   discuss or confirm vulnerabilities until a full investigation has
   occurred and any necessary patch(es) or release streams are available
   for all vulnerable and supported IRIX operating systems. Until SGI has
   more definitive information to provide, customers are encouraged to
   assume all security vulnerabilities as exploitable and take
   appropriate steps according to local site security policies and
   requirements. As further information becomes available, additional
   advisories will be issued via the normal SGI security information
   distribution methods including the wiretap mailing list on
   http://www.sgi.com/support/security/.

XFree86

   XFree86 versions 4.0 through 4.2.0 include zlib version 1.0.8. XFree86
   3.x includes zlib version 1.0.4. The zlib code included with XFree86
   is only used on some platforms. This is determined by the setting of
   HasZlib in the imake config files in the xc/config/cf source
   directory. If HasZlib is set to YES in the platform's vendor.cf
   file(s), then the system-provided zlib is used instead of the
   XFree86-provided version. XFree86 uses the system-provided zlib by
   default only on the following platforms:

     FreeBSD 2.2 and later
     NetBSD 1.2.2 and later
     OpenBSD
     Darwin
     Debian Linux

   The zlib code in XFree86 has been fixed in the CVS repository (trunk
   and the xf-4_2-branch branch) as of 14 February 2002. A source patch
   for XFree86 4.2.0 will be available from
   ftp://ftp.xfree86.org/pub/XFree86/4.2.0/fixes/.

   The following XFree86 4.2.0 binary distributions provided by XFree86
   include and use a vulnerable version of zlib:

     Linux-alpha-glibc22
     Linux-ix86-glibc22

   When updated binaries are available, it'll be documented at
   http://www.xfree86.org/4.2.0/UPDATES.html.

   To check if an installation of XFree86 includes zlib, see if the
   following file exists:

     /usr/X11R6/lib/libz.a

   To check if an XFree86 X server is dynamically linked with zlib, look
   for a line containing 'libz' in the output of 'ldd
   /usr/X11R6/bin/XFree86'.

   Various vendors repackage and distribute XFree86, and may use settings
   and configurations different from those described here.

zlib.org

   All users of zlib versions 1.1.3 or earlier should obtain the latest
   version, 1.1.4 or later, from http://www.zlib.org, in order to avoid
   this vulnerability as well as other possible vulnerabilities in
   versions prior to 1.1.3 when decompressing invalid data.

Appendix B. - References

     * http://bugzilla.gnome.org/show_bug.cgi?id=70594
     * http://www.kb.cert.org/vuls/id/368819
     * http://www.libpng.org/pub/png/pngapps.html
     * http://www.redhat.com/support/errata/RHSA-2002-026.html
     _________________________________________________________________

   The CERT/CC thanks Owen Taylor and Mark Cox of Red Hat, Inc. for
   reporting this vulnerability. We also thank Mark Adler of zlib.org for
   contributing to our research and Matthias Clasen for contributing to
   the discovery of this vulnerability.
     _________________________________________________________________

   This document was written by Jeffrey P. Lanza.
   ______________________________________________________________________

   This document is available from:
   http://www.cert.org/advisories/CA-2002-07.html
   ______________________________________________________________________

CERT/CC Contact Information

   Email: certcert.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
          U.S.A.

   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
   during other hours, on U.S. holidays, and on weekends.

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   If you prefer to use DES, please call the CERT hotline for more
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Getting security information

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   Patent and Trademark Office.
   ______________________________________________________________________

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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
Mar 12, 2002: Initial release

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