USN-5259-1 fixed several vulnerabilities in Cron. This update provides the corresponding update for Ubuntu 18.04 LTS.
Original advisory details:
It was discovered that the postinst maintainer script in Cron unsafely handled file permissions during package install or update operations. An attacker could possibly use this issue to perform a privilege escalation attack. (CVE-2017-9525)
Florian Weimer discovered that Cron incorrectly handled certain memory operations during crontab file creation. An attacker could possibly use this issue to cause a denial of service. (CVE-2019-9704)
It was discovered that Cron incorrectly handled user input during crontab file creation. An attacker could possibly use this issue to cause a denial of service. (CVE-2019-9705)
It was discovered that Cron contained a use-after-free vulnerability in its forcerescanuser function. An attacker could possibly use this issue to cause a denial of service. (CVE-2019-9706)