Chkrootkit 0.49 – Local Privilege Escalation
We just found a serious vulnerability in the chkrootkit package, which may allow local attackers to gain root access to a box in certain configurations (/tmp not mounted noexec). The vulnerability is located in the function slapper() in the shellscript chkrootkit: # # SLAPPER.{A,B,C,D} and the multi-platform variant # slapper (){ SLAPPER_FILES="${ROOTDIR}tmp/.bugtraq ${ROOTDIR}tmp/.bugtraq.c" SLAPPER_FILES="$SLAPPER_FILES ${ROOTDIR}tmp/.unlock ${ROOTDIR}tmp/httpd \ ${ROOTDIR}tmp/update ${ROOTDIR}tmp/.cinik ${ROOTDIR}tmp/.b"a SLAPPER_PORT="0.0:2002 |0.0:4156 |0.0:1978 |0.0:1812 |0.0:2015 " OPT=-an STATUS=0 file_port= if ${netstat} "${OPT}"|${egrep} "^tcp"|${egrep} "${SLAPPER_PORT}"> /dev/null 2>&1 then STATUS=1 [ "$SYSTEM" = "Linux" ] && file_port=`netstat -p ${OPT} | \ $egrep ^tcp|$egrep "${SLAPPER_PORT}" | ${awk} '{ print $7 }' | tr -d :` fi for i in ${SLAPPER_FILES}; do if [ -f ${i} ]; then file_port=$file_port $i STATUS=1 fi done if [ ${STATUS} -eq 1 ] ;then echo "Warning: Possible Slapper Worm installed ($file_port)" else if [ "${QUIET}" != "t" ]; then echo "not infected"; fi return ${NOT_INFECTED} fi } The line 'file_port=$file_port $i' will execute all files specified in $SLAPPER_FILES as the user chkrootkit is running (usually root), if $file_port is empty, because of missing quotation marks around the variable assignment. Steps to reproduce: - Put an executable file named 'update' with non-root owner in /tmp (not mounted noexec, obviously) - Run chkrootkit (as uid 0) Result: The file /tmp/update will be executed as root, thus effectively rooting your box, if malicious content is placed inside the file. If an attacker knows you are periodically running chkrootkit (like in cron.daily) and has write access to /tmp (not mounted noexec), he may easily take advantage of this. Suggested fix: Put quotation marks around the assignment. file_port="$file_port $i" I will also try to contact upstream, although the latest version of chkrootkit dates back to 2009 - will have to see, if I reach a dev there. |