USN-5259-3: Cron regression

Releases

• Ubuntu 18.04 ESM
• Ubuntu 16.04 ESM

Packages

• 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

• cron - 3.0pl1-128.1ubuntu1.2

Ubuntu 16.04

• cron - 3.0pl1-128ubuntu2+esm2
  Available with Ubuntu Pro

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

References

• CVE-2017-9525
• https://ubuntu.com/security/notices/USN-5259-2
• https://launchpad.net/bugs/1971895

Related notices

• USN-5259-1: cron
• USN-5259-2: cron