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