[ SOURCE: http://www.secureroot.com/security/advisories/9761547855.html ] Title: apcupsd 3.7.2 Denial of Service Affected Application: apcupsd daemon Affected Versions: 3.7.2 and maybe prior Not affected: 3.8.0 and above Affected Platforms: all Linux / Unix Vulnerability Class: Denial of Service (local) Author Notified: Yes July 12th 2000 Fix available: Yes (included) Description: Apcupsd is a daemon for controlling most of APC's UPS models on Unix and Windows machines. The Unix daemon runs as root and shuts the machine down in case of a power failure. Problem: During startup apcupsd creates a PID-file named "apcupsd.pid" in /var/run (system specific, maybe other directory) with the ID of the daemon process, this PID-file is used by the shutdown-script to kill the daemon process. Unfortunatly this PID-file ist world-writeable (Mode 666, -rw-rw-rw). A malicious user can overwrite the file with arbitrary process ID's, these processes will be killed instead of the apcupsd process during restart or stop of the apcupsd daemon and during system shutdown or restart, the whole system can be crashed this way. Solution: Upgrade to apcupsd Version 3.8.0 . It's available at: http://www.sibbald.com/apcupsd/ http://www.oasi.gpa.it/riccardo/linux/apcupsd/ ftp://ftp.oasi.gpa.it/pub/apcupsd/ User's who don't want to upgrade can add two lines to the "start" section in the apcupsd startup script in /etc/rc.d or /sbin/init.d : ---begin--- start) rm -f /etc/apcupsd/powerfail rm -f /etc/nologin echo -n "Starting apcupsd power management" $APCUPSD || return=$rc_failed # give the daemon some little time to create the PID-file sleep 1 #now simply chmod the PID-file to Mode 644 chmod 644 /var/run/apcupsd.pid echo -e "$return" ;; ---end--- Mattias Dartsch matze@joonix.de