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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 

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 1.1.22.8.17, 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

system.



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:



http://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-3-stable/comms/mgetty-1.1.22.8.17.tgz

http://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-4-stable/comms/mgetty-1.1.22.8.17.tgz

http://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-4-stable/comms/mgetty-1.1.22.8.17.tgz

http://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-5-current/comms/mgetty-1.1.22.8.17.tgz

http://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-5-current/comms/mgetty-1.1.22.8.17.tgz



3) download a new port skeleton for the mgetty 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:



http://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-3-stable/devel/portcheckout-2.0.tgz

http://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-4-stable/devel/portcheckout-2.0.tgz

http://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-4-stable/devel/portcheckout-2.0.tgz

http://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-5-current/devel/portcheckout-2.0.tgz

http://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-5-current/devel/portcheckout-2.0.tgz



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