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FreeBSD Ports Security Advisory: FreeBSD-SA-01:03.bash1
From: FreeBSD Security Advisories <security-advisories () freebsd org>
Date: Mon, 15 Jan 2001 14:31:17 -0800

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=============================================================================
FreeBSD-SA-01:03                                            Security Advisory
                                                                FreeBSD, Inc.

Topic:          bash1 creates insecure temporary files

Category:       ports
Module:         bash1
Announced:      2001-01-15
Affects:        Ports collection prior to the correction date.
Corrected:      2000-11-29
Credits:        Various
FreeBSD only:   NO

I.   Background

bash is an enhanced bourne-like shell.

II.  Problem Description

The bash port, versions prior to the correction date, creates insecure
temporary files when the '<<' operator is used, by using a predictable
filename based on the process ID of the shell.  An attacker can
exploit this vulnerability to overwrite an arbitrary file writable by
the user running the shell.  The contents of the file are overwritten
with the text being entered using the '<<' operator, so it will
usually not be under the control of the attacker.

Therefore the likely impact of this vulnerability is a denial of
service since the attacker can cause critical files writable by the
user to be overwritten.  It is unlikely, although possible depending
on the circumstances in which the '<<' operator is used, that the
attacker could exploit the vulnerability to gain privileges (this
typically requires that they have control over the contents the target
file is overwritten with).

This is the same vulnerability as that described in advisory 00:76
relating to the tcsh/csh shells.

The bash1 port is not installed by default, nor is it "part of
FreeBSD" as such: it is part of the FreeBSD ports collection, which
contains nearly 4500 third-party applications in a ready-to-install
format. The ports collections shipped with FreeBSD 3.5.1 and 4.2 are
vulnerable to this problem since it was discovered after the releases.

FreeBSD makes no claim about the security of these third-party
applications, although an effort is underway to provide a security
audit of the most security-critical ports.

III. Impact

Unprivileged local users can cause an arbitrary file writable by a
victim to be overwritten when the victim invokes the '<<' operator in
bash1 (e.g. from within a shell script).

If you have not chosen to install the bash1 port/package, then your
system is not vulnerable to this problem.

IV.  Workaround

Deinstall the bash1 port/package, if you have installed it.

V.   Solution

One of the following:

1) Upgrade your entire ports collection and rebuild the bash1 port.

2) Deinstall the old package and install a new package dated after the
correction date, obtained from the following directories:

ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-3-stable/shells/bash-1.14.7.tgz
ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-4-stable/shells/bash-1.14.7.tgz
ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-4-stable/shells/bash-1.14.7.tgz
ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-5-current/shells/bash-1.14.7.tgz
ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-5-current/shells/bash-1.14.7.tgz

NOTE: Due to an oversight the package version was not updated after
the security fix was applied, so be sure to install a package created
after the correction date.

3) download a new port skeleton for the bash1 port from:

http://www.freebsd.org/ports/

and use it to rebuild the port.

4) Use the portcheckout utility to automate option (3) above. The
portcheckout port is available in /usr/ports/devel/portcheckout or the
package can be obtained from:

ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-3-stable/devel/portcheckout-2.0.tgz
ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-4-stable/devel/portcheckout-2.0.tgz
ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-4-stable/devel/portcheckout-2.0.tgz
ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-5-current/devel/portcheckout-2.0.tgz
ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-5-current/devel/portcheckout-2.0.tgz
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