[UNIX] LutelWall Insecure Temporary File Creation

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To: list@securiteam.com
Date: 12 Jun 2005 14:11:42 +0200

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  LutelWall Insecure Temporary File Creation
------------------------------------------------------------------------

SUMMARY

" <http://firewall.lutel.pl/index.php> LutelWall is high-level Linux
firewall configuration tool. It uses human-readable and easy to understand
configuration to set up Netfilter in most secure way. Its flexibility
allows firewall administrators build from very simple, single-homed
firewalls, to most complex ones - with multiple subnets, DMZ's and traffic
redirections.

LutelWall firewall stores temporary files in an insecure way, which can be
exploited via symlink attacks to create and overwrite arbitrary files with
the privileges of the user running the affected script.

DETAILS

Vulnerable Systems:
 * LutelWall version 0.97 and prior

The exploitation requires that the root try to update the software.

Vulnerable Code:
# Prefix of temporary firewall files
tmp='/tmp/lutelwall'

new_version_check () { # Check for new version of script

  if [ "`wget -V 2>&1 >/dev/null`" ]; then
   message 3 "Warrning: Wget is required to check for updates."
  else
   new_ver=`wget -C off -O - -q -t 1 -T 3 -w 3 -U "\`uname -a 2>&1\`"
http://firewall.lutel.pl/ver`
   if [ `echo $current_version | gawk '{ gsub("\\\.","") ; print 1$0 }'`
-lt `echo $new_ver | gawk '{ gsub("\\\.","") ; print 1$0 }'` ]; then
    echo -e "\nThere is newer version of LutelWall (${new_ver})"
    echo -n " Changes since previous version:"
    echo `wget -C off -O $tmp-newfeat -q -t 1 -T 3 -w 3
http://firewall.lutel.pl/FEATURES-${new_ver}`
    cat $tmp-newfeat
    echo "Do you want to update [y/N]? "
    read -s -t 5 -n 1 ln
    if [ "$ln" = 'y' -o "$ln" = 'Y' ]; then
     wget -O $tmp-script -q -T 3 http://firewall.lutel.pl/lutelwall
     cat $tmp-script > $0
     rm -rf $tmp-script
     echo "Your firewall is up to date, exiting after update!"
     exit
    else
     message 5 "Update aborted"
    fi
   else
     message 5 "LutelWall is up-to-date"
   fi;
  fi;
}

Disclosure Timeline:
 * 22.05.05 - Vulnerability discovered
 * 22.05.05 - Vendor notified
 * 06.06.04 - Public disclosure

ADDITIONAL INFORMATION

The information has been provided by <mailto:exploits@zataz.net> ZATAZ
Audits.
The original article can be found at:
<http://www.zataz.net/adviso/lutelwall-05222005.txt>
http://www.zataz.net/adviso/lutelwall-05222005.txt

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