A sudo security update has been released for Ubuntu Linux 16.04 LTS, 18.04 LTS, 20.04 LTS, and 20.10.

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Ubuntu Security Notice USN-4705-1
January 26, 2021

sudo vulnerabilities
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 20.10
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS

Summary:

Several security issues were fixed in Sudo.

Software Description:
- sudo: Provide limited super user privileges to specific users

Details:

It was discovered that Sudo incorrectly handled memory when parsing command
lines. A local attacker could possibly use this issue to obtain unintended
access to the administrator account. (CVE-2021-3156)

It was discovered that the Sudo sudoedit utility incorrectly handled
checking directory permissions. A local attacker could possibly use this
issue to bypass file permissions and determine if a directory exists or
not. (CVE-2021-23239)

Update instructions:

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

Ubuntu 20.10:
sudo 1.9.1-1ubuntu1.1
sudo-ldap 1.9.1-1ubuntu1.1

Ubuntu 20.04 LTS:
sudo 1.8.31-1ubuntu1.2
sudo-ldap 1.8.31-1ubuntu1.2

Ubuntu 18.04 LTS:
sudo 1.8.21p2-3ubuntu1.4
sudo-ldap 1.8.21p2-3ubuntu1.4

Ubuntu 16.04 LTS:
sudo 1.8.16-0ubuntu1.10
sudo-ldap 1.8.16-0ubuntu1.10

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

References:
  https://usn.ubuntu.com/4705-1
CVE-2021-23239, CVE-2021-3156

Package Information:
  https://launchpad.net/ubuntu/+source/sudo/1.9.1-1ubuntu1.1
  https://launchpad.net/ubuntu/+source/sudo/1.8.31-1ubuntu1.2
  https://launchpad.net/ubuntu/+source/sudo/1.8.21p2-3ubuntu1.4
  https://launchpad.net/ubuntu/+source/sudo/1.8.16-0ubuntu1.10