Ubuntu 20.04 LTS: USN-4424-1 Moderate: snapd Access Restrictions

ubuntu

July 15, 2020

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

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)

Topics Covered

security advisory DoS Ubuntu access restriction snapd external media

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.