|
|
| Applications |
| Mailing Lists |
| Miscellaneous |
| Operating Systems |
| Programming |
FreeBSD Security Advisory FreeBSD-SA-07:01.jail [REVISED]
Date: Wed Aug 01 2007 - 17:26:08 EDT
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
FreeBSD-SA-07:01.jail Security Advisory
The FreeBSD Project
Topic: Jail rc.d script privilege escalation
Category: core
Module: etc_rc.d
Announced: 2007-01-11
Credits: Dirk Engling
Affects: All FreeBSD releases since 5.3
Corrected: 2007-01-11 18:16:58 UTC (RELENG_6, 6.2-STABLE)
2007-01-11 18:17:24 UTC (RELENG_6_2, 6.2-RELEASE)
2007-01-11 18:18:08 UTC (RELENG_6_1, 6.1-RELEASE-p12)
2007-01-11 18:18:35 UTC (RELENG_6_0, 6.0-RELEASE-p17)
2007-08-01 20:47:13 UTC (RELENG_5, 5.5-STABLE)
2007-08-01 20:48:19 UTC (RELENG_5_5, 5.5-RELEASE-p15)
CVE Name: CVE-2007-0166
For general information regarding FreeBSD Security Advisories, including descriptions of the fields above, security branches, and the following sections, please visit <URL:http://security.FreeBSD.org/>.
0. Revision History
v1.0 2007-01-11 Initial release.
v1.1 2007-08-01 Corrected patch for FreeBSD 5.5.
I. Background
The jail(2) system call allows a system administrator to lock a process and all of its descendants inside an environment with a very limited ability to affect the system outside that environment, even for processes with superuser privileges. It is an extension of, but far more powerful than, the traditional UNIX chroot(2) system call.
The host's jail rc.d(8) script can be used to start and stop jails automatically on system boot/shutdown.
II. Problem Description
In multiple situations the host's jail rc.d(8) script does not check if a path inside the jail file system structure is a symbolic link before using the path. In particular this is the case when writing the output from the jail start-up to /var/log/console.log and when mounting and unmounting file systems inside the jail directory structure.
III. Impact
Due to the lack of handling of potential symbolic links the host's jail rc.d(8) script is vulnerable to "symlink attacks". By replacing /var/log/console.log inside the jail with a symbolic link it is possible for the superuser (root) inside the jail to overwrite files on the host system outside the jail with arbitrary content. This in turn can be used to execute arbitrary commands with non-jailed superuser privileges.
Similarly, by changing directory mount points inside the jail file system structure into symbolic links, it may be possible for a jailed attacker to mount file systems which were meant to be mounted inside the jail at arbitrary points in the host file system structure, or to unmount arbitrary file systems on the host system.
NOTE WELL: The above vulnerabilities occur only when a jail is being started or stopped using the host's jail rc.d(8) script; once started (and until stopped), running jails cannot exploit this.
IV. Workaround
If the sysctl(8) variable security.jail.chflags_allowed is set to 0 (the default), setting the "sunlnk" system flag on /var, /var/log, /var/log/console.log, and all file system mount points and their parent directories inside the jail(s) will ensure that the console log file and mount points are not replaced by symbolic links. If this is done while jails are running, the administrator must check that an attacker has not replaced any directories with symlinks after setting the "sunlnk" flag.
V. Solution
NOTE WELL: The solution described changes the default location of the "console.log" for jails from /var/log/console.log inside each jail to /var/log/jail_${jail_name}_console.log on host system. If this is a problem, it may be possible to create a hard link from the new position of the console log file to a location inside the jail. A new rc.conf(5) variable, jail_${jail_name}_consolelog, can be used to change the location of console.log files on a per-jail basis.
In addition, the solution described below does not fully secure jail configurations where two jails have overlapping directory trees and a file system is mounted inside the overlap. Overlapping directory trees can occur when jails share the same root directory; when a jail has a root directory which is a subdirectory of another jail's root directory; or when a part of the file system space of one jail is mounted inside the file system space of another jail, e.g., using nullfs or unionfs.
To handle overlapping jails safely the administrator must set the sysctl(8) variable security.jail.chflags_allowed to 0 (the default) and manually set the "sunlnk" file/directory flag on all mount points and all parent directories of mount points. If this is done while jails are running, the adminstrator must check that an attacker has not replaced any directories with symlinks after setting the "sunlnk" flag.
Perform one of the following:
- Upgrade your vulnerable system to 5-STABLE, or 6-STABLE, or to the RELENG_6_1, RELENG_6_0, or RELENG_5_5 security branch dated after the correction date.
- To patch your present system:
The following patches have been verified to apply to FreeBSD 5.5, 6.0, and 6.1 systems.
- Download the relevant patch from the location below, and verify the detached PGP signature using your PGP utility.
[FreeBSD 5.5]
# fetch http://security.FreeBSD.org/patches/SA-07:01/jail5.patch
# fetch http://security.FreeBSD.org/patches/SA-07:01/jail5.patch.asc
[FreeBSD 6.0]
# fetch http://security.FreeBSD.org/patches/SA-07:01/jail60.patch
# fetch http://security.FreeBSD.org/patches/SA-07:01/jail60.patch.asc
[FreeBSD 6.1]
# fetch http://security.FreeBSD.org/patches/SA-07:01/jail61.patch
# fetch http://security.FreeBSD.org/patches/SA-07:01/jail61.patch.asc
NOTE: The patch distributed at the time of the original advisory was incorrect for FreeBSD 5.5 (both RELENG_5 and RELENG_5_5). Systems to which the original patch was applied should be patched with the following corrective patch, which contains only the changes between the original and updated patch:
# fetch http://security.FreeBSD.org/patches/SA-07:01/jail5-correction.patch
# fetch http://security.FreeBSD.org/patches/SA-07:01/jail5-correction.patch.asc
b) Execute the following commands as root:
# cd /usr/src
# patch < /path/to/patch
# install -o root -g wheel -m 555 etc/rc.d/jail /etc/rc.d
VI. Correction details
The following list contains the revision numbers of each file that was corrected in FreeBSD.
Branch RevisionPath
- ------------------------------------------------------------------------- RELENG_5 src/etc/rc.d/jail 1.15.2.7 RELENG_5_5 src/UPDATING 1.342.2.35.2.15 src/sys/conf/newvers.sh 1.62.2.21.2.17 src/etc/rc.d/jail 1.15.2.5.2.2 RELENG_6 src/etc/rc.d/jail 1.23.2.9 RELENG_6_2 src/UPDATING 1.416.2.29.2.2 src/etc/rc.d/jail 1.23.2.7.2.1 RELENG_6_1 src/UPDATING 1.416.2.22.2.14 src/sys/conf/newvers.sh 1.69.2.11.2.14 src/etc/rc.d/jail 1.23.2.3.2.3 RELENG_6_0 src/UPDATING 1.416.2.3.2.22 src/sys/conf/newvers.sh 1.69.2.8.2.18 src/etc/rc.d/jail 1.23.2.2.2.1 - -------------------------------------------------------------------------
VII. References
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-0166
The latest revision of this advisory is available at
http://security.FreeBSD.org/advisories/FreeBSD-SA-07:01.jail.asc
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.7 (FreeBSD)
iD8DBQFGsPfrFdaIBMps37IRAgksAJ4yGy3zTBcr2N+TbDoTlN3aHUA8QQCgi/8B
It4pOMoA0QMzAp8HxUWo+xU=
=9tTT
-----END PGP SIGNATURE-----
Received on Wed Aug 1 17:58:35 2007
This archive was generated by hypermail 2.1.8 : Sun Oct 28 2007 - 06:10:40 EDT
|
Contact Us Legal Notices Order Services Online Pantek Home Privacy Policy IT news Site Map Pantek Library |