FreeBSD Ports Security Advisory: FreeBSD-SA-00:71.mgetty

FreeBSD Security Advisories security-advisories at
Mon Nov 20 13:27:43 PST 2000


FreeBSD-SA-00:71                                           Security Advisory
                                                                FreeBSD, Inc.

Topic:          mgetty can create or overwrite files

Category:       ports
Module:         mgetty
Announced:      2000-11-20
Credits:        Stan Bubrouski <satan at FASTDIAL.NET>
Affects:        Ports collection prior to the correction date.
Corrected:      2000-9-10
Vendor status:  Updated version released
FreeBSD only:   NO

I.   Background

mgetty is a replacement for the getty utility designed for use with
data and fax modems.

II.  Problem Description

The mgetty port, versions prior to, contains a
vulnerability that may allow local users to create or overwrite any
file on the system.  This is due to the faxrunqd daemon (which usually
runs as root) following symbolic links when creating a .last_run file
in the world-writable /var/spool/fax/outgoing/ directory.

This presents a denial of service attack since the attacker can cause
critical system files to be overwritten, but it is not believed the
attacker has the ability to control the contents of the overwritten
file.  Therefore the possibility of using this attack to elevate
privileges is believed to be minimal.

The mgetty port is not installed by default, nor is it "part of
FreeBSD" as such: it is part of the FreeBSD ports collection, which
contains over 4100 third-party applications in a ready-to-install
format.  The ports collections shipped with FreeBSD 3.5.1 and 4.1.1
contain this problem since it was discovered after the releases, but
it was corrected prior to the release of FreeBSD 4.2.

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 may create or overwrite any file on the

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

IV.  Workaround

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

V.   Solution

One of the following:

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

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

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

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:

Version: GnuPG v1.0.4 (FreeBSD)
Comment: For info see


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