From proff Wed May 22 00:16:32 1996 Received: (proff@localhost) by suburbia.net (8.7.4/Proff-950810) id AAA07458 for best-of-security; Wed, 22 May 1996 00:16:32 +1000 Received: from melbourne.world.net (melbourne.world.net [198.142.2.1]) by suburbia.net (8.7.4/Proff-950810) with ESMTP id AAA07395 for ; Wed, 22 May 1996 00:12:52 +1000 Received: from why.cert.org (why.cert.org [192.88.209.31]) by melbourne.world.net (8.7.4/8.6.6) with SMTP id AAA09769 for ; Wed, 22 May 1996 00:14:12 +1000 (EST) Received: (from cert-advisory@localhost) by why.cert.org (8.6.12/CERT-ecd.1) id JAA28448 for cert-advisory-queue-4; Tue, 21 May 1996 09:17:29 -0400 Date: Tue, 21 May 1996 09:17:29 -0400 Message-Id: <199605211317.JAA28448@why.cert.org> From: CERT Bulletin To: cert-advisory@cert.org Subject: CERT Vendor-Initiated Bulletin VB-96.07 - FreeBSD (system stability compromise) Reply-To: cert-advisory-request@cert.org Organization: CERT(sm) Coordination Center - +1 412-268-7090 Sender: proff -----BEGIN PGP SIGNED MESSAGE----- ============================================================================= CERT(sm) Vendor-Initiated Bulletin VB-96.07 May 21, 1996 Topic: system stability compromise via mount_union program Source: The FreeBSD Project, Inc. To aid in the wide distribution of essential security information, the CERT Coordination Center is forwarding the following information from the Free BSD Project, Inc. The FreeBSD Project urges you to act on this information as soon as possible. Their contact information is included in the forwarded text below; please contact them if you have any questions or need further information. ========================FORWARDED TEXT STARTS HERE============================ ============================================================================= FreeBSD-SA-96:10 Security Advisory The FreeBSD Project, Inc. Topic: system stability compromise via mount_union program Category: core Module: unionfs Announced: 1996-05-17 Affects: FreeBSD 2.0, 2.0.5, 2.1, 2.1-stable, and 2.2-current Corrected: (workaround) 2.1-stable and 2.2-current as of 1996-05-17 Source: 4.4BSD (lite) FreeBSD only: no Patches: ftp://freebsd.org/pub/CERT/patches/SA-96:10/ ============================================================================= I. Background A bug was found in the union file system code which can allow an unprivileged local user to compromise system stability. This problem is present in all source code and binary distributions of FreeBSD version 2.x released before 1996-05-18. All FreeBSD users are encouraged to use the workaround provided until the FreeBSD Project distributes a full solution. II. Problem Description The union filesystem code had problems with certain mount ordering problems. By executing a certain sequence of mount_union commands, an unprivileged local user may cause a system reload. NOTE: This is a different problem than the one discussed in FreeBSD SA-96:09. The workaround for this vulnerability is similar to the one discussed in 96:09, but the proper solution for the unauthorized access problem in 96:09 does not address this vulnerability. III. Impact The problem could allow local users to compromise system stability. This vulnerability can only be exploited by users with a valid account on the local system. IV. Solution(s) The FreeBSD project is currently developing a solution to this problem, however the proper solution will not be available until a future FreeBSD release. We do not anticipate releasing patches for previous versions of FreeBSD due to the extensive nature of this fix. This security advisory will be updated as new information is made available. V. Workaround This vulnerability can quickly and easily be limited by removing the setuid permission bit from the mount_union program. This workaround will work for all versions of FreeBSD affected by this problem. As root, execute the command: % chmod u-s /sbin/mount_union then verify that the setuid permissions of the files have been removed. The permissions array should read "-r-xr-xr-x" as shown here: % ls -l /sbin/mount_union -r-xr-xr-x 1 root bin 53248 Apr 26 04:40 /sbin/mount_union In addition to changing the permissions on the executable files, if you have the source code installed, we suggest patching the sources so that mount_union will not be installed with the setuid bit set: *** /usr/src/sbin/mount_union/Makefile Sun Nov 20 14:47:52 1994 --- /usr/src/sbin/mount_union/Makefile Fri May 17 10:36:09 1996 *************** *** 8,14 **** CFLAGS+= -I${.CURDIR}/../../sys -I${MOUNT} .PATH: ${MOUNT} - BINOWN= root - BINMODE=4555 - .include --- 8,11 ---- ============================================================================= The FreeBSD Project, Inc. Web Site: http://www.freebsd.com/ Confidential contacts: security-officer@freebsd.org PGP Key: ftp://freebsd.org/pub/CERT/public_key.asc Security notifications: security-notifications@freebsd.org Security public discussion: security@freebsd.org Notice: Any patches in this document may not apply cleanly due to modifications caused by digital signature or mailer software. Please reference the URL listed at the top of this document for original copies of all patches if necessary. ============================================================================= =========================FORWARDED TEXT ENDS HERE============================= If you believe that your system has been compromised, contact the CERT Coordination Center or your representative in the Forum of Incident Response and Security Teams (FIRST). We strongly urge you to encrypt any sensitive information you send by email. The CERT Coordination Center can support a shared DES key and PGP. Contact the CERT staff for more information. Location of CERT PGP key ftp://info.cert.org/pub/CERT_PGP.key CERT Contact Information - ------------------------ Email cert@cert.org Phone +1 412-268-7090 (24-hour hotline) CERT personnel answer 8:30-5:00 p.m. EST (GMT-5)/EDT(GMT-4), and are on call for emergencies during other hours. Fax +1 412-268-6989 Postal address CERT Coordination Center Software Engineering Institute Carnegie Mellon University Pittsburgh PA 15213-3890 USA CERT publications, information about FIRST representatives, and other security-related information are available from http://www.cert.org/ ftp://info.cert.org/pub/ CERT advisories and bulletins are also posted on the USENET newsgroup comp.security.announce To be added to our mailing list for CERT advisories and bulletins, send your email address to cert-advisory-request@cert.org CERT is a service mark of Carnegie Mellon University. -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQCVAwUBMaG4/nVP+x0t4w7BAQENJQP+OHXfr3rAdi6OaHY2b0VOI2ul8rZ5/dLV 8hHsO9xjU0z7kv+2hCDttEqYKfbfItrOPA+lTcx3VweKlFQZJI7hwqEneddzd4wB b9FTjJNGzDBl+FgpD8vwHxxiTZ70AYg2vYeOYpvaFB982Z47NxXogre4DXv6r2Y9 DaauaJRNuyg= =rSaQ -----END PGP SIGNATURE-----