-----BEGIN PGP SIGNED MESSAGE----- ============================================================================= FreeBSD-SA-02:18 Security Advisory FreeBSD, Inc. Topic: zlib double-free Category: core, ports Module: zlib Announced: 2002-03-18 Revised: 2002-04-22 Credits: Matthias Clasen Owen Taylor Affects: All released versions of FreeBSD FreeBSD 4.5-STABLE prior to the correction date Various ports using or including zlib Corrected: 2002-02-24 23:12:48 UTC (RELENG_4) 2002-02-24 23:22:57 UTC (RELENG_4_5) 2002-02-24 23:23:58 UTC (RELENG_4_4) 2002-02-24 23:24:46 UTC (RELENG_4_3) CVE: CAN-2002-0059 FreeBSD only: NO 0. Revision History v1.0 2002-03-18 Initial release v1.1 2002-04-18 Corrected ZFREE location in kernel patch Corrected deflate window size check v1.2 2002-04-22 Corrected advisory revision dates. I. Background zlib is a compression library used by numerous applications to provide data compression/decompression routines. II. Problem Description A programming error in zlib may cause segments of dynamically allocated memory to be released more than once (double-freed). 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 may cause the zlib routines to attempt to free memory multiple times. Unlike some implementations of malloc(3)/free(3), the malloc(3) and free(3) routines used in FreeBSD (aka phkmalloc, written by Poul-Henning Kamp ), are not vulnerable to this type of bug. From the author: Most mallocs keep their housekeeping data right next to the allocated range. This gives rise to all sorts of unpleassant situations if programs stray outside the dotted line, free(3) things twice or free(3) modified pointers. phkmalloc(3) does not store housekeeping next to allocated data, and in particular it has code that detects and complains about exactly this kind of double free. When attempting to double-free an area of memory, phkmalloc will issue a warning: progname in free(): error: chunk is already free and may call abort(3) if the malloc flag 'A' is used. III. Impact If an attacker is able to pass a specially-crafted block of invalid compressed data to an application that utilizes zlib, the attempt to decompress the data may cause incorrect operation of the application, including possibly crashing the application. Also, the malloc implementation will issue warnings and, if the `A' malloc option is used, cause the application to abort(3). In short, an attacker may cause a denial of service in applications utilizing zlib. IV. Workaround To prevent affected programs from aborting, remove the 'A' from the malloc flags. To check which malloc flags are in use, issue the following commands: # ls -l /etc/malloc.conf # echo $MALLOC_OPTIONS A nonexistent /etc/malloc.conf or MALLOC_OPTIONS environmental variable means that no malloc flags are in use. See the malloc(3) man page for more information. V. Solution [FreeBSD 4.x base system] 1) Upgrade your vulnerable system to 4.5-STABLE or to one of the RELENG_4_4 or RELENG_4_5 security branches dated after the respective correction dates. 2) To patch your present system: download the relevant patch from the below location, and execute the following commands as root: For FreeBSD 4.x systems that have the previous zlib patch applied: # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:18/zlib.v1.1.corrected.patch # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:18/zlib.v1.1.corrected.patch.asc For FreeBSD 4.x systems that do not have the previous zlib patch applied: # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:18/zlib.v1.1.patch # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:18/zlib.v1.1.patch.asc Verify the detached PGP signature using your PGP utility. This patch has been verified to apply to all FreeBSD 4.x versions. # cd /usr/src # patch -p < /path/to/patch # cd lib/libz # make depend && make all install Then rebuild and reinstall your kernel as described in http://www.freebsd.org/handbook/kernelconfig.html and reboot the system with the new kernel for the changes to take effect. [ports] Various ports may statically link zlib or contain their own versions of zlib that have not been corrected by updating the FreeBSD libz. Efforts are underway to identify and correct these ports. VI. Correction details The following list contains the revision numbers of each file that was corrected in FreeBSD. Path Revision Branch - ------------------------------------------------------------------------- src/lib/libz/deflate.c RELENG_4 1.5.2.1 RELENG_4_5 1.5.8.1 RELENG_4_4 1.5.6.1 RELENG_4_3 1.5.4.1 src/lib/libz/infblock.c RELENG_4 1.1.1.4.6.1 RELENG_4_5 1.1.1.4.12.1 RELENG_4_4 1.1.1.4.10.1 RELENG_4_3 1.1.1.4.8.1 src/sys/net/zlib.c RELENG_4 1.10.2.3 RELENG_4_5 1.10.8.2 RELENG_4_4 1.10.6.2 RELENG_4_3 1.10.4.2 - ------------------------------------------------------------------------- VII. References The Common Vulnerabilities and Exposures project (cve.mitre.org) has assigned the name CAN-2002-0059 to this issue. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (FreeBSD) Comment: For info see http://www.gnupg.org iQCVAwUBPMQkDVUuHi5z0oilAQEWKAP+OT1w4Nilf/mfBjXu9xFPeRRyyKaq8ALX Hmm2XQ3plhUsqjFupYxdss5+PuIhT7OiLoc8n+B7n8DjjTtGEK/Ds7/iBlox+b+3 JhhE4HBbwLDMpQ9VSI36iV4qr7YuNZbpCCrAG85bOIhWQDRdc+IWkdxW4P0flhAm 42eaFTWtbB4= =QAcg -----END PGP SIGNATURE-----