A python-apt update has been released for Ubuntu Linux 19.10, 19.04, 18.04 LTS, and 16.04 LTS to address several security issues.

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Ubuntu Security Notice USN-4247-1
January 22, 2020

python-apt vulnerabilities
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 19.10
- Ubuntu 19.04
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS

Summary:

Several security issues were fixed in python-apt.

Software Description:
- python-apt: Python interface to libapt-pkg

Details:

It was discovered that python-apt would still use MD5 hashes to validate
certain downloaded packages. If a remote attacker were able to perform a
man-in-the-middle attack, this flaw could potentially be used to install
altered packages. (CVE-2019-15795)

It was discovered that python-apt could install packages from untrusted
repositories, contrary to expectations. (CVE-2019-15796)

Update instructions:

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

Ubuntu 19.10:
python-apt 1.9.0ubuntu1.2
python3-apt 1.9.0ubuntu1.2

Ubuntu 19.04:
python-apt 1.8.5~ubuntu0.2
python3-apt 1.8.5~ubuntu0.2

Ubuntu 18.04 LTS:
python-apt 1.6.5ubuntu0.1
python3-apt 1.6.5ubuntu0.1

Ubuntu 16.04 LTS:
python-apt 1.1.0~beta1ubuntu0.16.04.7
python3-apt 1.1.0~beta1ubuntu0.16.04.7

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

References:
  https://usn.ubuntu.com/4247-1
CVE-2019-15795, CVE-2019-15796

Package Information:
  https://launchpad.net/ubuntu/+source/python-apt/1.9.0ubuntu1.2
  https://launchpad.net/ubuntu/+source/python-apt/1.8.5~ubuntu0.2
  https://launchpad.net/ubuntu/+source/python-apt/1.6.5ubuntu0.1
  https://launchpad.net/ubuntu/+source/python-apt/1.1.0~beta1ubuntu0.16.04.7