A snapd regression update has been released for Ubuntu Linux 14.04 ESM, 16.04 ESM, 18.04 LTS, 20.04 LTS, and 21.10.

USN-5292-4: snapd regression

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Ubuntu Security Notice USN-5292-4
February 24, 2022

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

- Ubuntu 21.10
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS
- Ubuntu 16.04 ESM
- Ubuntu 14.04 ESM

Summary:

USN-5292-1 introduced a regression in snapd.

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

Details:

USN-5292-1 fixed a vulnerability in snapd. Unfortunately that update introduced
a regression that could break the fish shell. This update fixes the problem.

We apologize for the inconvenience.

Original advisory details:

James Troup discovered that snap did not properly manage the permissions for
the snap directories. A local attacker could possibly use this issue to expose
sensitive information. (CVE-2021-3155)

Ian Johnson discovered that snapd did not properly validate content interfaces
and layout paths. A local attacker could possibly use this issue to inject
arbitrary AppArmor policy rules, resulting in a bypass of intended access
restrictions. (CVE-2021-4120)

The Qualys Research Team discovered that snapd did not properly validate the
location of the snap-confine binary. A local attacker could possibly use this
issue to execute other arbitrary binaries and escalate privileges.
(CVE-2021-44730)

The Qualys Research Team discovered that a race condition existed in the snapd
snap-confine binary when preparing a private mount namespace for a snap. A
local attacker could possibly use this issue to escalate privileges and
execute arbitrary code. (CVE-2021-44731)

Update instructions:

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

Ubuntu 21.10:
snap-confine 2.54.3+21.10.1ubuntu0.2
snapd 2.54.3+21.10.1ubuntu0.2

Ubuntu 20.04 LTS:
snap-confine 2.54.3+20.04.1ubuntu0.2
snapd 2.54.3+20.04.1ubuntu0.2

Ubuntu 18.04 LTS:
snap-confine 2.54.3+18.04.2ubuntu0.2
snapd 2.54.3+18.04.2ubuntu0.2

Ubuntu 16.04 ESM:
snap-confine 2.54.3+16.04.0ubuntu0.1~esm4
snapd 2.54.3+16.04.0ubuntu0.1~esm4

Ubuntu 14.04 ESM:
snap-confine 2.54.3+14.04.0ubuntu0.1~esm3
snapd 2.54.3+14.04.0ubuntu0.1~esm3

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

References:
  https://ubuntu.com/security/notices/USN-5292-4
  https://ubuntu.com/security/notices/USN-5292-1
  https://bugs.launchpad.net/ubuntu/+source/snapd/+bug/1961365,   https://bugs.launchpad.net/ubuntu/+source/snapd/+bug/1961791

Package Information:
  https://launchpad.net/ubuntu/+source/snapd/2.54.3+21.10.1ubuntu0.2
  https://launchpad.net/ubuntu/+source/snapd/2.54.3+20.04.1ubuntu0.2
  https://launchpad.net/ubuntu/+source/snapd/2.54.3+18.04.2ubuntu0.2