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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://launchpad.net/bugs/1971895
CVE-2017-9525

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