=========================================================================Ubuntu Security Notice USN-5259-3
May 11, 2022

cron regression
=========================================================================
A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 18.04 LTS
- Ubuntu 16.04 ESM

Summary:

USN-5259-1 and USN-5259-2 introduced a regression in Cron.

Software Description:
- cron: process scheduling daemon

Details:

USN-5259-1 and USN-5259-2 fixed vulnerabilities in Cron. Unfortunately
that update was incomplete and could introduce a regression. This update
fixes the problem.

We apologize for the inconvenience.

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 force_rescan_user function. An attacker could possibly use this issue
  to cause a denial of service. (CVE-2019-9706)

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 18.04 LTS:
   cron                            3.0pl1-128.1ubuntu1.2

Ubuntu 16.04 ESM:
   cron                            3.0pl1-128ubuntu2+esm2

In general, a standard system update will make all the necessary changes.

References:
   https://ubuntu.com/security/notices/USN-5259-1
   https://ubuntu.com/security/notices/USN-5259-2
   https://ubuntu.com/security/notices/USN-5259-3
   https://bugs.launchpad.net/ubuntu/+source/cron/+bug/1971895
   CVE-2017-9525

Package Information:
   https://launchpad.net/ubuntu/+source/cron/3.0pl1-128.1ubuntu1.2