[NEWS] Double Free Bug in zlib Compression Library
From: support@securiteam.comDate: 03/12/02
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From: support@securiteam.com To: list@securiteam.com Date: Tue, 12 Mar 2002 22:21:11 +0100 (CET)
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Double Free Bug in zlib Compression Library
------------------------------------------------------------------------
SUMMARY
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 CERT at
this time, it is difficult to determine whether this bug can be
successfully exploited. However, given the widespread deployment of
zlib, CERT has published this document as a proactive measure.
DETAILS
Vulnerable systems:
* 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
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.
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.
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> http://www.zlib.org.
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.
Vendor Information:
This section contains information provided by vendors for this
advisory.
If a particular vendor is not listed below, CERT/CC has not received
their comments.
Apple Computer, Inc.
Mac OS X and Mac OS X Server do not contain this vulnerability.
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.
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>
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>
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/>
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/>
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>
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.
ADDITIONAL INFORMATION
The information has been provided by <mailto:cert@cert.org> CERT/CC.
References:
* <http://bugzilla.gnome.org/show_bug.cgi?id=70594>
http://bugzilla.gnome.org/show_bug.cgi?id=70594
* <http://www.kb.cert.org/vuls/id/368819>
http://www.kb.cert.org/vuls/id/368819
* <http://www.libpng.org/pub/png/pngapps.html>
http://www.libpng.org/pub/png/pngapps.html
* <http://www.redhat.com/support/errata/RHSA-2002-026.html>
http://www.redhat.com/support/errata/RHSA-2002-026.html
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