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CERT Vendor-Initiated Bulletin VB-95:07 - lsof
====================================================================== CERT Vendor-Initiated Bulletin VB-95:07 September 28, 1995 Topic: Directory and file vulnerability from lsof 3.18 through 3.43 Source: Vic Abell ([email protected]) To aid in the wide distribution of essential security information, the CERT Coordination Center is forwarding the following information from Vic Abell, who urges you to act on this information as soon as possible. Please contact Vic Abell if you have any questions or need further information. ========================FORWARDED TEXT STARTS HERE============================ It may be possible to write lsof's private device cache file to system locations that are normally inaccessible to the lsof user, depending on the UNIX dialect where lsof is installed and how that dialect grants permission to access kernel memory information. The vulnerability affects lsof revisions 3.18 through 3.43, installed on these UNIX dialects: AIX 3.2.4, 3.2.5, 4.1, the IBM RISC/System 6000 4.1.1, and 4.1.2 EP/IX 2.1.1 the CDC 4680 FreeBSD 22.214.171.124, 2.0, and Intel-based systems 2.0.5 HP-UX 8.x, 9.x, and 10 HP systems (some combinations) IRIX 4.0.5H, 5.2, 5.3, SGI systems 6.0, and 6.1 Linux through 1.3.0 Intel-based systems Motorola V/88 R32V3, M88K systems R40V4. NetBSD 1.0 and 1.0A Intel and SPARC-based systems NEXTSTEP 2.1 and 3. all NEXTSTEP architectures OSF/1 1.3, 2.0, 3.0, and the DEC Alpha 3.2 RISC/os 4.52 MIPS R2000-based systems SCO OpenDesktop or Intel-based systems OpenServer 1.1, 3.0, and 5.0 Sequent Dynix 3.0.12 the Sequent Symmetry Sequent PTX 2.1. and Sequent systems 4.0. Solaris 2. and 2.5 Sun 4 and i86pc systems BETA SunOS 4.1. Sun 3 and 4 Ultrix 2.2, 4.2, 4.3, DEC RISC and VAX and 4.4 I recommend that users of the affected revisions of lsof on these dialects install lsof revision 3.44, 3.45 or later. Section III describes its location and some appropriate installation considerations. ----------------------------------------------------------------------------- I. Description A private device cache file feature was introduced at lsof revision 3.18 to speed up subsequent calls to lsof by reducing the need for a full scan of the nodes in /dev (or /devices). Accompanying the feature was an option (-D) that allowed the lsof user to specify where the device cache file was to be recorded. Since lsof normally runs with effective group ID permission set to the group that can read kernel memory devices, the -D option might allow lsof to write its device cache file to a location not normally accessible to the real user or group owning the lsof process. The locations where the lsof device cache file might be inappropriately recorded depend on the group that owns the memory devices and to what other files and directories the group has write permission. Here are two examples: 1) IBM's distribution of AIX sets group ownership of /dev/kmem and /etc to the "system" group and enables group write permission in /etc; and 2) Sun's Solaris distribution does the same thing, using the "sys" group. (Security conscious installations often create a new group -- e.g., "kmem" or "mem" -- that owns no files and is used solely for enabling read access to kernel memory devices.) A fix for this group ID vulnerability may be found in lsof revisions 3.44, 3.45, and above. A more serious vulnerability exists when lsof must run setuid to the root user and also has device cache file support. This happens for the lsof implementation that runs under Motorola's V/88 UNIX dialects R40V4.1, R40V4.2, and R40V4.3. This gives the lsof user an unlimited choice of places to record the device cache file. A partial fix for this vulnerability was introduced in lsof revision 3.43. The complete fix may be found in lsof revisions 3.44, 3.45, and above. II. Impact Unauthorized users may be able to write the lsof device cache file to normally-restricted locations, possibly in place of important system files. The vulnerability can be exploited only by users with a valid account. It cannot be exploited by arbitrary remote users. The vulnerability affects all lsof revisions 3.18 through 3.43 on UNIX dialects where device cache file support has been implemented. III. Solution Retrieve lsof revision 3.44, 3.45, or later and install it. Compressed tar archive: ftp://vic.cc.purdue.edu/pub/tools/unix/lsof/lsof.tar.Z Gzip'd tar archive: ftp://vic.cc.purdue.edu/pub/tools/unix/lsof/lsof.tar.gz Lsof 3.44 eliminates the vulnerability for all relevant UNIX dialects. However, its overly zealous restrictions for Solaris and SunOS and are relaxed in revision 3.45. Both tar archives are wrappers that contain authentication information (MD5 checksums and PGP certificates) and a tar archive of the lsof sources. 1. Retrieve the wrapper archive, extract its three files -- README.lsof_<revision>, lsof_<revision>.tar, and lsof_<revision>.tar.asc -- and verify its authentication information. (<revision> should be 3.44 or greater.) 2. Unpack the lsof source archive from lsof_<revision>.tar and read its documentation files. Pay particular attention to the 00DCACHE file that describes options for specifying the location of the device cache, and the security section in the 00README file. 3. Having selected the lsof options appropriate to the UNIX dialect where you want to install it, run the Configure script, use make to build lsof, and install the resulting lsof executable. ----------------------------------------------------------------------------- Vic Abell appreciates the advice and comments provided by members of the bugtraq mailing list that led him to realize this vulnerability existed. He thanks Katherine T. Fithen and Linda Hutz Pesante of the CERT Coordination Center for their help in preparing this bulletin. =========================FORWARDED TEXT ENDS HERE============================= CERT publications, information about FIRST representatives, and other information related to computer security are available for anonymous FTP from info.cert.org. CERT advisories and bulletins are also posted on the USENET newsgroup comp.security.announce. If you would like to have future advisories and bulletins mailed to you or to a mail exploder at your site, please send mail to [email protected] If you wish to send sensitive incident or vulnerability information to CERT staff by electronic mail, we strongly advise that the e-mail be encrypted. The CERT Coordination Center can support a shared DES key, PGP (public key available via anonymous FTP on info.cert.org), or PEM (contact CERT staff for details). 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