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Zlib Advisory 2002-03-11
zlib Compression Library Corrupts malloc Data Structures via Double Free
Original release date: March 11, 2002
Last revised: March 11, 2002
Source: This advisory is based on a CERT advisory written
by Jeffrey P. Lanza. See original on http://www.cert.org
Systems Affected
* Any software that is linked against zlib 1.1.3 or earlier
* Any data compression library derived from zlib 1.1.3 or earlier
Overview
There is a vulnerability in the zlib shared library that may introduce
vulnerabilities into any program that includes zlib. This
vulnerability has been assigned a CVE candidate name of CAN-2002-0059
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2002-0059
I. Description
There is a vulnerability 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 vulnerability results from a programming error that causes
segments of dynamically allocated memory to be released more than once
(aka. "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 vulnerability interferes with the proper allocation and
de-allocation 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.
II. Impact
This vulnerability 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. Any software that is linked against or derived from an
earlier version of zlib should be upgraded immediately. The latest
version of zlib is available at http://www.zlib.org
The md5 sums of the source archives are:
abc405d0bdd3ee22782d7aa20e440f08 zlib-1.1.4.tar.gz
ea16358be41384870acbdc372f9db152 zlib-1.1.4.tar.bz2
IV. Acknowledgments
Thanks to Owen Taylor and other people at Redhat Inc. for the
reporting and research of this vulnerability.
This document is available from
http://www.gzip.org/zlib/advisory-2002-03-11.txt
The public PGP key of zlib author Jean-loup Gailly is available from
http://www.gzip.org/zlib/jloup.asc
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