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TUCoPS :: Unix :: General :: m-062.txt

Double Free Bug in zlib Compression Library (CIAC M-062)




             __________________________________________________________

                       The U.S. Department of Energy
                     Computer Incident Advisory Center
                           ___  __ __    _     ___
                          /       |     /_\   /
                          \___  __|__  /   \  \___
             __________________________________________________________

                             INFORMATION BULLETIN

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

March 22, 2002 22:00 GMT                                          Number M-062
______________________________________________________________________________
PROBLEM:       There is a bug in the zlib compression library that may 
               manifest itself as a vulnerability in programs that are linked 
               with zlib. This bug may allow an attacker to conduct a 
               denial-of-service attack, have the capability to gather 
               information, or execute arbitrary code.
PLATFORM:      * 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.
DAMAGE:        If this vulnerability is exploited, an attacker may conduct a 
               denial-of-service, gather information, or execute arbitrary 
               code.
SOLUTION:      See CERT's vendor list for affected products and apply 
               appropriate patch.
______________________________________________________________________________
VULNERABILITY  The risk is MEDIUM. Currently, there are no widespread reports 
ASSESSMENT:    of exploitation of this vulnerability. However, 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. 
______________________________________________________________________________
LINKS: 
 CIAC BULLETIN:      http://www.ciac.org/ciac/bulletins/m-062.shtml 
 ORIGINAL BULLETIN:  http://www.cert.org/advisories/CA-2002-07.html 
______________________________________________________________________________

Revision History:
[Revision 04/03/02: CISCO Systems, Hewlett-Packard, and Juniper Networks 
                    release vendor updates]
[Revision 11/20/02: Sun Microsystems Security Bulletin #00220 Releases
                    Latest Updates for Java(TM) Runtime Environment (JRE)] 
                    http://www.sunsolve.sun.com/pub-cgi/
                    retrieve.pl?doctype=coll&doc=secbull/220&type=0&nav=sec.sba

[***** Start CERT Advisory CA-2002-07 *****]

CERTŪ Advisory CA-2002-07 Double Free Bug in zlib Compression Library
Original release date: March 12, 2002
Last revised: March 21, 2002 1410 EST
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 

The maintainers of zlib have published an advisory regarding this issue; 
for further information, please see 

http://www.gzip.org/zlib/advisory-2002-03-11.txt

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. 

Cisco Systems

Cisco Systems is addressing the vulnerability identified by VU#368819 across 
all affected products.  Cisco has released an advisory:
  http://www.cisco.com/warp/public/707/zlib-double-free.shtml

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.

Debian

Users of Debian GNU/Linux 2.2 (potato) should upgrade to zlib 
version 1.1.3-5.1.  More information is available at 
http://www.debian.org/security/2002/dsa-122. Note that a few packages 
which include private copies of zlib will also need to be 
upgraded--more information is available at the above link.

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.

F-Secure Corporation

F-Secure SSH is not vulnerable to zlib double free bug.

No version of F-Secure SSH software is vulnerable to the "Double 
Free Bug in zlib Compression Library" discussed in CERT Advisory 
CA-2002-07.

All F-Secure SSH versions, both the old SSH1 and later SSH2 protocol 
clients and servers, close connection immediately with fatal cleanup 
call without any further calls to zlib when call to zlib's inflate() 
returns something else than Z_OK.

Fujitsu

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

Hewlett-Packard Company

HP-UX products currently use the 1.0.8 version of zlib and are not vulnerable 
to the reported double free problem.  The possibility of other vulnerabilities 
in 1.0.8 is being investigated.  

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.

Juniper Networks

Juniper Networks has completed an initial assessment of this vulnerability, 
and we believe that our implementation is not susceptible.  Test programs 
show that our memory allocation algorithm correctly detects and warns about
any attempt to exploit the vulnerability described in the CERT/CC advisory.

We continue to evaluate the risks associated with this vulnerability.  If we
determine that the JUNOS software is susceptible, we will quickly issue any 
patches or software updates required to maintain the security of Juniper 
Networks routers.

Future JUNOS software releases will include a corrected version of the libz 
code.

Microsoft Corporation

Microsoft is currently conducting a full investigation based on the 
information provided by CERT.

NetBSD

NetBSD's malloc libraries are not vulnerable to double-free() attacks. 
The updated zlib will be included in future releases, but a Security 
Advisory will not be issued.

Novell, Inc.

Novell is working on a fix for Novell JVM for NetWare 1.3.1.  We will post 
the fix in the May NDK.  Version 1.4 will also have the fix in it.  We will 
also update this statement with the URL to download the fix.

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 haveidentified 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 a
vailable 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/.

SSH Communications Security

SSH Secure Shell is not vulnerable to zlib double free bug. 

No version of SSH Secure Shell software is vulnerable to the 
"Double Free Bug in zlib Compression Library" discussed in CERT 
Advisory CA-2002-07.

All SSH Secure Shell versions, including SSH2 protocol clients 
and servers, close the connection immediately with a fatal cleanup 
call without any further calls to zlib when a call to zlib's 
inflate() returns something else than Z_OK.

Standard Networks, Inc.

Standard Networks offers a "mainframe connectivity" product 
called "OpenIT" which uses the zlib library to compress ("zip") 
files transferred between Unisys mainframes and remote FTP clients 
and servers. After a code analysis we found the zlib vulnerability 
does not affect this product.

Standard Networks also offers a secure HTTPS-based file transfer 
client called "MOVEit Wizard" which uses the zlib library to compress 
("zip") files transferred between MOVEit DMZ servers and remote 
browsers. After a code analysis we found the zlib vulnerability does 
not affect this product.

Nonetheless, Standard Networks will use "corrected" versions of 
zlib in future versions of both products.

No other Standard Networks products ("ActiveHEAT","EMU","MOVEit DMZ", 
"MOVEit Central", "MOVEit Admin", "MOVEit Freely", "MOVEit Buddy", 
"Unigate") are affected.

Customers are encouraged to call Standard Networks immediately 
(+001 608.227.6100) with any questions or concerns about their specific 
configuration.

Sun Microsystems, Inc.

Solaris 8 includes the zlib library as part of the SUNWzlib package 
which is affected by this issue. Sun is generating patches for zlib 
presently. When patches are available, Sun will publish a Sun Security 
Bulletin.

Sun is investigating what other Sun products or applications may be 
impacted which use a private copy of zlib or code from the zlib library.

Sun Security Bulletins are available from: 

http://sunsolve.sun.com/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.gzip.org/zlib/advisory-2002-03-11.txt 
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 
http://www.securityfocus.com/bid/4267

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

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

[***** End CERT Advisory CA-2002-07 *****]

_______________________________________________________________________________

CIAC wishes to acknowledge the contributions of CERT Coordination Center for the 
information contained in this bulletin.
_______________________________________________________________________________


CIAC, the Computer Incident Advisory Center, is the computer
security incident response team for the U.S. Department of Energy
(DOE) and the emergency backup response team for the National
Institutes of Health (NIH). CIAC is located at the Lawrence Livermore
National Laboratory in Livermore, California. CIAC is also a founding
member of FIRST, the Forum of Incident Response and Security Teams, a
global organization established to foster cooperation and coordination
among computer security teams worldwide.

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can be contacted at:
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Previous CIAC notices, anti-virus software, and other information are
available from the CIAC Computer Security Archive.

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PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing
communities receive CIAC bulletins.  If you are not part of these
communities, please contact your agency's response team to report
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constituencies can be obtained via WWW at http://www.first.org/.

This document was prepared as an account of work sponsored by an
agency of the United States Government. Neither the United States
Government nor the University of California nor any of their
employees, makes any warranty, express or implied, or assumes any
legal liability or responsibility for the accuracy, completeness, or
usefulness of any information, apparatus, product, or process
disclosed, or represents that its use would not infringe privately
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