Ensure at/cron is restricted to authorized users

MediumLevel 1Automatedlinux

Description

Configure /etc/cron.allow and /etc/at.allow to allow specific users to use these services. If /etc/cron.allow or /etc/at.allow do not exist, then /etc/at.deny and /etc/cron.deny are checked. Any user not specifically defined in those files is allowed to use at and cron. By removing the files, only users in /etc/cron.allow and /etc/at.allow are allowed to use at and cron. Note that even though a given user is not listed in cron.allow , cron jobs can still be run as that user. The cron.allow file only controls administrative access to the crontab command for scheduling and modifying cron jobs.

How it is checked

Audit method: Shell command

shell

alt0() { command -v stat >/dev/null 2>&1 || { echo "step1: stat not installed"; return 1; }; o=$(bash -c 'stat /etc/cron.deny' 2>&1); printf '%s\n' "$o" | tr -s ' \t' '  ' | sed 's/^ //;s/ $//' | grep -Fxq -- 'stat: cannot stat `/etc/cron.deny'"'"': No such file or directory' || { echo step1: missing 'stat: cannot stat `/etc/cron.deny'"'"': No such file or director'; return 1; }; command -v stat >/dev/null 2>&1 || { echo "step2: stat not installed"; return 1; }; o=$(bash -c 'stat /etc/at.deny' 2>&1); printf '%s\n' "$o" | tr -s ' \t' '  ' | sed 's/^ //;s/ $//' | grep -Fxq -- 'stat: cannot stat` /etc/at.deny'"'"': No such file or directory' || { echo step2: missing 'stat: cannot stat` /etc/at.deny'"'"': No such file or directory'; return 1; }; command -v stat >/dev/null 2>&1 || { echo "step3: stat not installed"; return 1; }; o=$(bash -c 'stat /etc/cron.allow' 2>&1); printf '%s\n' "$o" | tr -s ' \t' '  ' | sed 's/^ //;s/ $//' | grep -Fxq -- 'Access: (0600/-rw-------) Uid: ( 0/ root) Gid: ( 0/ root)' || { echo step3: missing 'Access: (0600/-rw-------) Uid: ( 0/ root) Gid: ( 0/ root)'; return 1; }; command -v stat >/dev/null 2>&1 || { echo "step4: stat not installed"; return 1; }; o=$(bash -c 'stat /etc/at.allow' 2>&1); printf '%s\n' "$o" | tr -s ' \t' '  ' | sed 's/^ //;s/ $//' | grep -Fxq -- 'Access: (0600/-rw-------) Uid: ( 0/ root) Gid: ( 0/ root)' || { echo step4: missing 'Access: (0600/-rw-------) Uid: ( 0/ root) Gid: ( 0/ root)'; return 1; }; }; if alt0; then echo compliant; fi

Expected output: compliant

How it is fixed

Fix method: Guidance or infrastructure patch

Run the following commands to remove /etc/cron.deny and /etc/at.deny and create and set permissions and ownership for /etc/cron.allow and /etc/at.allow : # rm /etc/cron.deny # rm /etc/at.deny # touch /etc/cron.allow # touch /etc/at.allow # chmod 600 /etc/cron.allow # chmod 600 /etc/at.allow # chown root:root /etc/cron.allow # chown root:root /etc/at.allow

Properties

Operating systems: alinux-2
Tags: cis-convertedlinux
Reference: CIS Aliyun Linux 2 Benchmark v1.0.0 ARCHIVE - 5.1.8

Check this host

Run this on a machine you are allowed to audit. The scan is read-only.

shell

tmaegis scan --target linux