[USN-4424-1] snapd vulnerabilities

[Emilia Torino]

==========================================================================
Ubuntu Security Notice USN-4424-1
July 15, 2020

snapd vulnerabilities
==========================================================================

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

- Ubuntu 20.04 LTS
- Ubuntu 19.10
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS

Summary:

An intended access restriction in snapd could be bypassed by strict mode
snaps.

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

Details:

It was discovered that cloud-init as managed by snapd on Ubuntu Core 16
and Ubuntu Core 18 devices ran on every boot without restrictions. A
physical attacker could exploit this to craft cloud-init
user-data/meta-data via external media to perform arbitrary changes on
the device to bypass intended security mechanisms such as full disk
encryption. This issue did not affect traditional Ubuntu systems.
(CVE-2020-11933)

It was discovered that snapctl user-open allowed altering the
XDG_DATA_DIRS environment variable when calling the system xdg-open. A
malicious snap could exploit this to bypass intended access restrictions
to control how the host system xdg-open script opens the URL. This issue
did not affect Ubuntu Core systems. (CVE-2020-11934)

Update instructions:

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

Ubuntu 20.04 LTS:
  snapd                           2.45.1+20.04.2

Ubuntu 19.10:
  snapd                           2.45.1+19.10.2

Ubuntu 18.04 LTS:
  snapd                           2.45.1+18.04.2

Ubuntu 16.04 LTS:
  snapd                           2.45.1ubuntu0.2

In general, a standard system update will make all the necessary changes.
On Ubuntu, snapd will automatically refresh itself to snapd 2.45.2 which
is unaffected.

References:
  https://usn.ubuntu.com/4424-1
  CVE-2020-11933, CVE-2020-11934

Package Information:
  https://launchpad.net/ubuntu/+source/snapd/2.45.1+20.04.2
  https://launchpad.net/ubuntu/+source/snapd/2.45.1+19.10.2
  https://launchpad.net/ubuntu/+source/snapd/2.45.1+18.04.2
  https://launchpad.net/ubuntu/+source/snapd/2.45.1ubuntu0.2

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