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

USN-4951-1: Flatpak vulnerability

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Ubuntu Security Notice USN-4951-1
May 12, 2021

flatpak vulnerability
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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

Summary:

A Flatpak application could access files that it would not normally
be permitted to access.

Software Description:
- flatpak: Application deployment framework for desktop apps

Details:

Anton Lydike discovered that Flatpak did not properly handle special tokens
in desktop files. An attacker could use this to specially craft a Flatpak
application that could escape sandbox confinement.

Update instructions:

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

Ubuntu 20.10:
flatpak 1.8.2-1ubuntu0.2
libflatpak0 1.8.2-1ubuntu0.2

Ubuntu 20.04 LTS:
flatpak 1.6.5-0ubuntu0.3
libflatpak0 1.6.5-0ubuntu0.3

Ubuntu 18.04 LTS:
flatpak 1.0.9-0ubuntu0.3
libflatpak0 1.0.9-0ubuntu0.3

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

References:
  https://ubuntu.com/security/notices/USN-4951-1
CVE-2021-21381

Package Information:
  https://launchpad.net/ubuntu/+source/flatpak/1.8.2-1ubuntu0.2
  https://launchpad.net/ubuntu/+source/flatpak/1.6.5-0ubuntu0.3
  https://launchpad.net/ubuntu/+source/flatpak/1.0.9-0ubuntu0.3