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=============================================================================

FreeBSD-SA-00:46                                           Security Advisory

                                                                FreeBSD, Inc.



Topic:          screen port contains local root compromise



Category:       ports

Module:         screen

Announced:      2000-09-12

Affects:        Ports collection prior to the correction date.

Corrected:      2000-09-01

Credits:        Jouko Pynnönen 

Vendor status:  Updated version released

FreeBSD only:   NO



I.   Background



screen is a popular application that multiplexes a physical terminal

between several processes.



II.  Problem Description



The screen port, versions 3.9.5 and before, contains a vulnerability

which allows local users to gain root privileges.  This is

accomplished by inserting string-formatting operators into

configuration parameters, which may allow arbitrary code to be

executed.



The screen 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 3800 third-party applications in a ready-to-install

format. The ports collections shipped with FreeBSD 3.5.1 and 4.1

contain 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



Local users can obtain root privileges.



If you have not chosen to install the screen port/package, then your

system is not vulnerable to this problem.



IV.  Workaround



Remove the setuid bit on the program: execute the following command as

root:



chmod 555 /usr/local/bin/screen-3.9.5



Note that this should be considered a temporary measure and may affect

the behaviour of the screen program.



V.   Solution



One of the following:



1) Upgrade your entire ports collection and rebuild the screen 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/misc/screen-3.9.8.tgz

http://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-4-stable/misc/screen-3.9.8.tgz

http://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-4-stable/misc/screen-3.9.8.tgz

http://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-5-current/misc/screen-3.9.8.tgz

http://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-5-current/misc/screen-3.9.8.tgz



NOTE: It may be several days before updated packages are available.



3) download a new port skeleton for the screen 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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