Fw: CIAC Bulletin H-67: Red Hat Linux X11 Libraries Buffer Overflow

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Sun Jun 1 11:08:48 EEST 1997

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From: CIAC Mail User <ciac at tholia.llnl.gov>
To: ciac-bulletin at tholia.llnl.gov
Date: Saturday, May 31, 1997 9:12 PM
Subject: CIAC Bulletin H-67: Red Hat Linux X11 Libraries Buffer Overflow

>             __________________________________________________________
>                       The U.S. Department of Energy
>                    Computer Incident Advisory Capability
>                           ___  __ __    _     ___
>                          /       |     /_\   /
>                          \___  __|__  /   \  \___
>             __________________________________________________________
>                             INFORMATION BULLETIN
>                    Red Hat Linux X11 Libraries Buffer Overflow
>May 30, 1997 22:00 GMT                                             Number
>PROBLEM:       A problem has been identified in the X11 libraries that
>               a buffer overflow condition.
>PLATFORM:      This problem affects all Red Hat Linux machines with X
>               installed.
>DAMAGE:        This vulnerability allows local users to gain unauthorized
>               access to a system.
>SOLUTION:      Apply the necessary patches indicated below.
>VULNERABILITY  Information involving this vulnerability has been made
>ASSESSMENT:    available.
>[  Start Linux Security Alert ]
>     Buffer overflow in the resource handling code of the libXt (X11R6)
>                              Thu May 29, 1997
>                 Distribution of this document is unlimited
>              Copyright (C) Alexander O. Yuriev (alex at yuriev.com)
>                                 Net Access
>     A buffer overflow was found in the resource handling section of the
>     system (libXt). As this is a problem with libXt iself, every program
>     using libXt is affected, including core programs such as xterm and
>     programs derived from it. Of course only suid and sgid programs can
>     exploited to gain access to gain extra priviledges.
>Permanent Solution
>     The permanent solution requires fixing the libXt. It is recommended
>     that you utilize temporary solution. This buffer overflow does not
>     exist in XFree86 3.3 code. It is recommended that you upgrade to
>     XFree86 3.3 as soon as it becomes available.
>     Currently fixed versions of fixed libraries are available for:
>        o Red Hat Linux 4.0, 4.1, 4.2 from Red Hat Software
>Temporary solution
>     The workaround requires identifying and temporary disabling suid
>     programs in the X11R6 tree. The following sequence of commands can
>     used to find all suid and sgid programs of the X11 tree:
>          $ cd /usr/X11/bin
>          $ find . -type f -a \( -perm -2000 -o -perm -4000 \) -print
>     As the output, these commands would produce a list of suid or sgid
>     programs in directories starting from the current working directory
>     (/usr/X11/bin) to the end of the tree. A typical output would look
>     like:
>          X
>          xterm
>          dga
>     Determine if you use every program in question. Look at the manual
>     pages to see if you really need it at this time. I personally have
>     idea why Red Hat did not remove the dga(1) program of the XFree86
>     distribution shipped with Red Hat 4.1 as dga(1) manual page states:
>          dga - test program for the Xfree86-DGA extension
>     Assuming that the DGA extension is required, the test program should
>     used only by "root". Therefore, the suid bit is not needed and
>     be removed. Same logic should be applied to other suid/sgid
>     At this time you probably should remove suid bit from the dga(1) or
>     least make it non-world executable. Use commands:
>          # chmod 111 dga
>          # chattr +I dga
>     to disable suid bit on a dga binary and make it immutable. Use the
>     method to evaluate all other suid programs.
>     Programs that should be run by root only, should never be suid to
>     or at least should not be world executable. X Display Manager,
>     falls into this category.
>     If you need the functionality provided by the vulnerable program,
>     disable execution for that program and add trusted accounts that
>     to run the program into the group which own the program. You must
>     realize that by doing this you are allowing those who have access to
>     the trusted accounts exploit the vulnerability and gain access to
>     euid of the program.
>XTERM(1) and xterm derived programs
>     Unfortunately, you cannot remove suid bit from the xterm(1) and
>     programs derived from it withot losing part of functionality. The
>     advice by authors of exploits from bugtraq to squash suid bit
>     xterm(1) from changing ownerships of tty devices allowing any user on
>     system to read information from terminal devices.
>     This looks like a lose-lose situation unless you are willing to
>     xterm(1) program completely (and leave with it being disabled )
>     the fixed version becomes available. Basically, you should consider
>     risks of someone from your system running xterm(1) and gaining root
>     access to a system vs. not being able to run xterm(1) at all and vs.
>     running xterm(1) as non-suid application which would allow one user
>     intercept keystrokes of another. It is your choice but no matter
>     you decide to do, think about the consequences first.
>Vendor fixes
>   * Red Hat Linux from Red Hat Software
>        o Red Hat Linux/Alpha 4.1, 4.2
>               ftp://ftp.redhat.com/updates/4.2/alpha/
>                     XFree86-devel-3.2-10.alpha.rpm
>               ftp://ftp.redhat.com/updates/4.2/alpha/
>                     XFree86-libs-3.2-10.alpha.rpm
>               ftp://ftp.aoy.com/pub/Linux/security/DISTRIBUTION-FIXES/
>                     RedHat/XFree86-devel-3.2-10.alpha.rpm
>               ftp://ftp.aoy.com/pub/Linux/security/DISTRIBUTION-FIXES/
>                     RedHat/XFree86-libs-3.2-10.alpha.rpm
>        o Red Hat Linux/Intel 4.0, 4.1, 4.2
>               ftp://ftp.redhat.com/updates/4.2/i386/
>                     XFree86-devel-3.2-10.i386.rpm
>               ftp://ftp.redhat.com/updates/4.2/i386/
>                     XFree86-libs-3.2-10.i386.rpm
>               ftp://ftp.aoy.com/pub/Linux/security/DISTRIBUTION-FIXES/
>                     RedHat/XFree86-devel-3.2-10.i386.rpm
>               ftp://ftp.aoy.com/pub/Linux/security/DISTRIBUTION-FIXES/
>                     RedHat/XFree86-libs-3.2-10.i386.rpm
>        o Red Hat Linux/SPARC 4.0, 4.1, 4.2
>               ftp://ftp.redhat.com/updates/4.2/sparc/
>                     X11R6.1-devel-pl1-21.sparc.rpm
>               ftp://ftp.redhat.com/updates/4.2/sparc/
>                     X11R6.1-libs-pl1-21.sparc.rpm
>               ftp://ftp.aoy.com/pub/Linux/security/DISTRIBUTION-FIXES/
>                     RedHat/X11R6.1-devel-pl1-21.sparc.rpm
>               ftp://ftp.aoy.com/pub/Linux/security/DISTRIBUTION-FIXES/
>                     RedHat/X11R6.1-libs-pl1-21.sparc.rpm
>          Please verify the signature of RPMs using the rpm --checksig
>          command. The RPMs are signed with the PGP key of Red Hat
>          pub 1024/CBA29BF9 1996/02/20 Red Hat Software, Inc.
>          <redhat at redhat.com>
>     The exploits were posted in bugtraq mailing list by Ming Zhang. Erik
>     Troan (ewt at redhat.com) from Red Hat Software provided information
>     the XFree86 3.3, as well as fixes for the Red Hat Linux
>[ End Linux Security Alert ]
>CIAC wishes to acknowledge the contributions of Alexander O. Yuriev and
>for the information contained in this bulletin.
>CIAC, the Computer Incident Advisory Capability, is the computer
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