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Ubuntu Security Notice USN-4728-1
February 10, 2021

snapd 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
- Ubuntu 16.04 LTS

Summary:

An intended access restriction in snapd could be bypassed by container
management snaps.

Software Description:
- snapd: Daemon and tooling that enable snap packages

Details:

Gilad Reti discovered that snapd did not correctly specify cgroup
delegation when generating systemd service units for various container
management snaps. This could allow a local attacker to escalate privileges
via access to arbitrary devices of the container host from within a
compromised or malicious container.

Update instructions:

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

Ubuntu 20.10:
  snapd                           2.48.3+20.10

Ubuntu 20.04 LTS:
  snapd                           2.48.3+20.04

Ubuntu 18.04 LTS:
  snapd                           2.48.3+18.04

Ubuntu 16.04 LTS:
  snapd                           2.48.3

In general, a standard system update will make all the necessary changes.
On Ubuntu, snapd will automatically refresh itself to snapd 2.48.3 which is
unaffected. Affected container management snaps will also automatically
refresh which will restart containers and resolve this vulnerability.

References:
  https://usn.ubuntu.com/4728-1
  CVE-2020-27352

Package Information:
  https://launchpad.net/ubuntu/+source/snapd/2.48.3+20.10
  https://launchpad.net/ubuntu/+source/snapd/2.48.3+20.04
  https://launchpad.net/ubuntu/+source/snapd/2.48.3+18.04
  https://launchpad.net/ubuntu/+source/snapd/2.48.3