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=============================================================================
FreeBSD-SA-01:40 Security Advisory
FreeBSD, Inc.

Topic: fts(3) routines contain race condition [REVISED]

Category: core
Module: libc
Announced: 2001-06-04
Revised: 2001-08-16
Credits: Nick Cleaton <[email protected]>
Todd Miller <[email protected]> helped to develop the
patch.
Affects: FreeBSD 4.3-RELEASE, 4.3-STABLE prior to the correction
date.
Corrected: 2001-06-01
FreeBSD only: NO

0. Revision History

2001-06-04 v1.0 Initial release
2001-08-16 v1.1 Corrected typo in recompilation instructions

I. Background

The standard C library (libc) contains a set of routines known as fts
which allow an application to recursively traverse a filesystem.

II. Problem Description

The fts routines are vulnerable to a race condition when ascending a
file hierarchy, which allows an attacker who has control over part of
the hierarchy into which fts is descending to cause the application to
ascend beyond the starting point of the file traversal, and enter
other parts of the filesystem.

If the fts routines are being used by an application to perform
operations on the filesystem hierarchy, such as find(1) with a keyword
such as -exec or -delete, or rm(1) with the -r flag, these operations
can be incorrectly applied to files outside the intended hierarchy,
which may result in system damage or compromise.

All versions of FreeBSD prior to the correction date including
4.3-RELEASE are vulnerable to this problem.

III. Impact

Local users may be able to remove or modify files on the local system
which are owned or writable by a user running a command that uses the
FTS routines in a vulnerable way.

If the system administrator has enabled the daily_clean_tmps_enable
variable in /etc/periodic.conf, the find -delete command is run once
per day, allowing unauthorised removal of files on the system. This
option is not enabled by default.

IV. Workaround

None appopriate for the general vulnerability. The instance exposed
by the daily_clean_tmps_enable setting can be prevented by disabling
this switch in /etc/periodic.conf, if it has been enabled.

V. Solution

One of the following:

1) As of FreeBSD 4.3-RELEASE, we have introduced a new ``security fix
CVS branch'' which contains security fixes only, which can be tracked
using the standard FreeBSD tools (cvsup/CVS/etc). The branch name is
``RELENG_4_3''. Upgrade your vulnerable FreeBSD system to the
RELENG_4_3 branch after the correction date.

2) Upgrade your vulnerable FreeBSD system to 4.3-STABLE after the
correction dates.

3) To patch your present system: download the relevant patch from the
below location, and execute the following commands as root:

[FreeBSD 4.3 base system]

fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-01:40/fts.patch

fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-01:40/fts.patch.asc

Verify the detached PGP signature using your PGP utility.

cd /usr/src/lib/libc

patch -p < /path/to/patch

make depend && make all install

cd /usr/src/lib/libc_r

make depend && make all install

cd /usr/src/bin/chmod

make depend && make all install

cd /usr/src/bin/cp

make depend && make all install

cd /usr/src/bin/ls

make depend && make all install

cd /usr/src/bin/pax

make depend && make all install

cd /usr/src/bin/rm

make depend && make all install

cd /usr/src/usr.bin/chflags

make depend && make all install

cd /usr/src/usr.bin/du

make depend && make all install

cd /usr/src/usr.bin/find

make depend && make all install

cd /usr/src/libexec/ftpd

make depend && make all install

cd /usr/src/usr.sbin/chown

make depend && make all install

cd /usr/src/usr.sbin/ckdist

make depend && make all install

cd /usr/src/usr.sbin/ctm

make depend && make all install

cd /usr/src/usr.sbin/mtree

make depend && make all install

cd /usr/src/usr.sbin/pkg_install

make depend && make all install

This patch has been verified to apply to FreeBSD 4.3-RELEASE and
4.2-RELEASE; it may or may not apply to older, unsupported versions of
FreeBSD.

4) An experimental upgrade package is available for adventurous users
who wish to provide testing and feedback on the binary upgrade
process. This package may be installed on FreeBSD 4.3-RELEASE systems
only, and is intended for use on systems for which source patching is
not practical or convenient.

Since this is the first binary upgrade package produced for the
FreeBSD base system, it is not recommended that this be used on
production systems without first being tested on a scratch machine;
since the package replaces critical system files, a failed upgrade can
leave a system in an unusable state.

During the installation procedure, backup copies are made of the files
which are replaced by the package. These backup copies will be
reinstalled if the package is removed, reverting the system to a
pre-patch state.

fetch

ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/packages/SA-01:40/security-patch-fts-01.40.tgz

fetch

ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/packages/SA-01:40/security-patch-fts-01.40.tgz.asc

Verify the detached PGP signature using your PGP utility.

Bring the system down to single-user mode; this package should not be
installed from multi-user mode. If it desired to remove the package
at a later date, you should again do so from single-user mode.

shutdown now

pkg_add security-patch-fts-01.40

Follow the directions given after the installation of the package to
complete the system upgrade.

To bring the system back up to multi-user mode, type the following
command:

exit

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