An OpenSSH security update has been released for Ubuntu Linux 14.04 LTS, 16.04 LTS, and 18.04 LTS.

[USN-6242-2] OpenSSH vulnerability

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Ubuntu Security Notice USN-6242-2
July 31, 2023

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

- Ubuntu 18.04 LTS (Available with Ubuntu Pro)
- Ubuntu 16.04 LTS (Available with Ubuntu Pro)
- Ubuntu 14.04 LTS (Available with Ubuntu Pro)

Summary:

OpenSSH could be made to run programs as your login when using ssh-agent
forwarding.

Software Description:
- openssh: secure shell (SSH) for secure access to remote machines

Details:

USN-6242-1 fixed a vulnerability in OpenSSH. This update provides
the corresponding update for Ubuntu 14.04 LTS, Ubuntu 16.04 LTS,
and Ubuntu 18.04 LTS.

Original advisory details:

It was discovered that OpenSSH incorrectly handled loading certain PKCS#11
providers. If a user forwarded their ssh-agent to an untrusted system, a
remote attacker could possibly use this issue to load arbitrary libraries
from the user's system and execute arbitrary code.

Update instructions:

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

Ubuntu 18.04 LTS (Available with Ubuntu Pro):
openssh-client 1:7.6p1-4ubuntu0.7+esm1

Ubuntu 16.04 LTS (Available with Ubuntu Pro):
openssh-client 1:7.2p2-4ubuntu2.10+esm3

Ubuntu 14.04 LTS (Available with Ubuntu Pro):
openssh-client 1:6.6p1-2ubuntu2.13+esm1

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

References:
https://ubuntu.com/security/notices/USN-6242-2
https://ubuntu.com/security/notices/USN-6242-1
CVE-2023-38408