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============================================================================= FreeBSD-SA-11:07.chroot Security Advisory The FreeBSD Project

Topic: Code execution via chrooted ftpd

Category: core Module: libc Announced: 2011-12-23 Affects: All supported versions of FreeBSD. Corrected: 2011-12-23 15:00:37 UTC (RELENG_7, 7.4-STABLE) 2011-12-23 15:00:37 UTC (RELENG_7_4, 7.4-RELEASE-p5) 2011-12-23 15:00:37 UTC (RELENG_7_3, 7.3-RELEASE-p9) 2011-12-23 15:00:37 UTC (RELENG_8, 8.2-STABLE) 2011-12-23 15:00:37 UTC (RELENG_8_2, 8.2-RELEASE-p5) 2011-12-23 15:00:37 UTC (RELENG_8_1, 8.1-RELEASE-p7) 2011-12-23 15:00:37 UTC (RELENG_9, 9.0-STABLE) 2011-12-23 15:00:37 UTC (RELENG_9_0, 9.0-RELEASE)

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/>.

I. Background

Chroot is an operation that changes the apparent root directory for the current process and its children. The chroot(2) system call is widely used in many applications as a measure of limiting a process's access to the file system, as part of implementing privilege separation.

The nsdispatch(3) API implementation has a feature to reload its configuration on demand. This feature may also load shared libraries and run code provided by the library when requested by the configuration file.

II. Problem Description

The nsdispatch(3) API has no mechanism to alert it to whether it is operating within a chroot environment in which the standard paths for configuration files and shared libraries may be untrustworthy.

The FreeBSD ftpd(8) daemon can be configured to use chroot(2), and also uses the nsdispatch(3) API.

III. Impact

If ftpd is configured to place a user in a chroot environment, then an attacker who can log in as that user may be able to run arbitrary code with elevated ("root") privileges.

IV. Workaround

Don't use ftpd with the chroot option.

V. Solution

Perform one of the following:

1) Upgrade your vulnerable system to 7-STABLE or 8-STABLE, or to the RELENG_8_2, RELENG_8_1, RELENG_7_4, or RELENG_7_3 security branch dated after the correction date.

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to FreeBSD 7.4, 7.3, 8.2 and 8.1 systems.

a) Download the relevant patch from the location below, and verify the detached PGP signature using your PGP utility.

[FreeBSD 7.3 and 7.4] # fetch http://security.FreeBSD.org/patches/SA-11:07/chroot7.patch # fetch http://security.FreeBSD.org/patches/SA-11:07/chroot7.patch.asc

[FreeBSD 8.1 and 8.2] # fetch http://security.FreeBSD.org/patches/SA-11:07/chroot8.patch # fetch http://security.FreeBSD.org/patches/SA-11:07/chroot8.patch.asc

b) Execute the following commands as root:

# cd /usr/src # patch < /path/to/patch

c) Recompile the operating system as described in <URL: http://www.freebsd.org/handbook/makeworld.html> and reboot the system.

3) To update your vulnerable system via a binary patch:

Systems running 7.4-RELEASE, 7.3-RELEASE, 8.2-RELEASE, or 8.1-RELEASE on the i386 or amd64 platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch # freebsd-update install

4) This update adds a new API, __FreeBSD_libc_enter_restricted_mode() to the C library, which completely disables loading of shared libraries upon return. Applications doing chroot(2) jails need to be updated to call this API explicitly right after the chroot(2) operation as a safety measure.

VI. Correction details

The following list contains the revision numbers of each file that was corrected in FreeBSD.

CVS:

Branch Revision Path - ------------------------------------------------------------------------- RELENG_7 src/include/unistd.h 1.80.2.4 src/lib/libc/include/libc_private.h 1.17.2.4 src/lib/libc/Versions.def 1.3.2.3 src/lib/libc/net/nsdispatch.c 1.14.2.3 src/lib/libc/gen/Symbol.map 1.6.2.7 src/lib/libc/gen/Makefile.inc 1.128.2.6 src/lib/libc/gen/libc_dlopen.c 1.2.2.2 src/libexec/ftpd/popen.c 1.26.10.2 src/libexec/ftpd/ftpd.c 1.212.2.2 RELENG_7_4 src/UPDATING 1.507.2.36.2.7 src/sys/conf/newvers.sh 1.72.2.18.2.10 src/include/unistd.h 1.80.2.3.4.2 src/lib/libc/include/libc_private.h 1.17.2.3.4.2 src/lib/libc/Versions.def 1.3.2.2.4.2 src/lib/libc/net/nsdispatch.c 1.14.2.2.2.2 src/lib/libc/gen/Symbol.map 1.6.2.6.4.2 src/lib/libc/gen/Makefile.inc 1.128.2.5.4.2 src/lib/libc/gen/libc_dlopen.c 1.2.4.2 src/libexec/ftpd/popen.c 1.26.10.1.2.2 src/libexec/ftpd/ftpd.c 1.212.2.1.6.2 RELENG_7_3 src/UPDATING 1.507.2.34.2.11 src/sys/conf/newvers.sh 1.72.2.16.2.13 src/include/unistd.h 1.80.2.3.2.2 src/lib/libc/include/libc_private.h 1.17.2.3.2.2 src/lib/libc/Versions.def 1.3.2.2.2.2 src/lib/libc/net/nsdispatch.c 1.14.2.1.6.2 src/lib/libc/gen/Symbol.map 1.6.2.6.2.2 src/lib/libc/gen/Makefile.inc 1.128.2.5.2.2 src/lib/libc/gen/libc_dlopen.c 1.1.2.1 src/libexec/ftpd/popen.c 1.26.24.2 src/libexec/ftpd/ftpd.c 1.212.2.1.4.2 RELENG_8 src/include/unistd.h 1.95.2.2 src/lib/libc/include/libc_private.h 1.20.2.3 src/lib/libc/Versions.def 1.8.2.3 src/lib/libc/net/nsdispatch.c 1.18.2.3 src/lib/libc/gen/Symbol.map 1.21.2.6 src/lib/libc/gen/Makefile.inc 1.144.2.7 src/lib/libc/gen/libc_dlopen.c 1.1.4.2 src/libexec/ftpd/popen.c 1.26.22.3 src/libexec/ftpd/ftpd.c 1.214.2.3 RELENG_8_2 src/UPDATING 1.632.2.19.2.7 src/sys/conf/newvers.sh 1.83.2.12.2.10 src/include/unistd.h 1.95.2.1.6.2 src/lib/libc/include/libc_private.h 1.20.2.2.4.2 src/lib/libc/Versions.def 1.8.2.2.4.2 src/lib/libc/net/nsdispatch.c 1.18.2.2.2.2 src/lib/libc/gen/Symbol.map 1.21.2.5.2.2 src/lib/libc/gen/Makefile.inc 1.144.2.6.2.2 src/lib/libc/gen/libc_dlopen.c 1.2.8.2 src/libexec/ftpd/popen.c 1.26.22.2.4.2 src/libexec/ftpd/ftpd.c 1.214.2.1.6.2 RELENG_8_1 src/UPDATING 1.632.2.14.2.10 src/sys/conf/newvers.sh 1.83.2.10.2.11 src/include/unistd.h 1.95.2.1.4.2 src/lib/libc/include/libc_private.h 1.20.2.2.2.2 src/lib/libc/Versions.def 1.8.2.2.2.2 src/lib/libc/net/nsdispatch.c 1.18.2.1.4.2 src/lib/libc/gen/Symbol.map 1.21.2.3.2.2 src/lib/libc/gen/Makefile.inc 1.144.2.4.2.2 src/lib/libc/gen/libc_dlopen.c 1.2.10.2 src/libexec/ftpd/popen.c 1.26.22.2.2.2 src/libexec/ftpd/ftpd.c 1.214.2.1.4.2 RELENG_9 src/include/unistd.h 1.101.2.2 src/lib/libc/include/libc_private.h 1.26.2.2 src/lib/libc/Versions.def 1.9.2.2 src/lib/libc/net/nsdispatch.c 1.19.2.2 src/lib/libc/gen/Symbol.map 1.38.2.2 src/lib/libc/gen/Makefile.inc 1.159.2.2 src/lib/libc/gen/libc_dlopen.c 1.1.6.2 src/lib/libc/iconv/citrus_module.c 1.1.2.2 src/libexec/ftpd/popen.c 1.27.2.2 src/libexec/ftpd/ftpd.c 1.220.2.2 RELENG_9_0 src/include/unistd.h 1.101.2.1.2.2 src/lib/libc/include/libc_private.h 1.26.2.1.2.2 src/lib/libc/Versions.def 1.9.2.1.2.2 src/lib/libc/net/nsdispatch.c 1.19.2.1.2.2 src/lib/libc/gen/Symbol.map 1.38.2.1.2.2 src/lib/libc/gen/Makefile.inc 1.159.2.1.2.2 src/lib/libc/gen/libc_dlopen.c 1.2.6.2 src/lib/libc/iconv/citrus_module.c 1.1.2.1.2.2 src/libexec/ftpd/popen.c 1.27.2.1.2.2 src/libexec/ftpd/ftpd.c 1.220.2.1.2.2 - -------------------------------------------------------------------------

Subversion:

Branch/path Revision - ------------------------------------------------------------------------- stable/7/ r228843 releng/7.4/ r228843 releng/7.3/ r228843 stable/8/ r228843 releng/8.2/ r228843 releng/8.1/ r228843 stable/9/ r228843 releng/9.0/ r228843 - -------------------------------------------------------------------------

VII. References

The latest revision of this advisory is available at http://security.FreeBSD.org/advisories/FreeBSD-SA-11:07.chroot.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.18 (FreeBSD)

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