Ubuntu 24.04 LTS, Ubuntu 22.04 LTS, and Ubuntu 20.04 LTS have received a security update to address a protocol issue in AsyncSSH that was revealed to be vulnerable to the Terrapin attack, potentially resulting in inferior algorithms:

[USN-7051-1] AsyncSSH vulnerability

[USN-7051-1] AsyncSSH vulnerability

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Ubuntu Security Notice USN-7051-1
October 02, 2024

python-asyncssh vulnerability
==========================================================================

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

- Ubuntu 24.04 LTS
- Ubuntu 22.04 LTS
- Ubuntu 20.04 LTS

Summary:

A protocol flaw was fixed in AsyncSSH.

Software Description:
- python-asyncssh: asyncio-based client and server implementation of SSHv2
protocol

Details:

Fabian Bäumer, Marcus Brinkmann, Jörg Schwenk discovered that the SSH
protocol was vulnerable to a prefix truncation attack. If a remote attacker
was able to intercept SSH communications, extension negotiation messages
could be truncated, possibly leading to certain algorithms and features
being downgraded. This issue is known as the Terrapin attack. This update
adds protocol extensions to mitigate this issue.

Update instructions:

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

Ubuntu 24.04 LTS
  python3-asyncssh                2.10.1-2ubuntu0.1

Ubuntu 22.04 LTS
  python3-asyncssh                2.5.0-1ubuntu0.1~esm1
                                  Available with Ubuntu Pro

Ubuntu 20.04 LTS
  python3-asyncssh                1.12.2-1ubuntu0.1

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

References:
  https://ubuntu.com/security/notices/USN-7051-1
  CVE-2023-48795

Package Information:
https://launchpad.net/ubuntu/+source/python-asyncssh/2.10.1-2ubuntu0.1
https://launchpad.net/ubuntu/+source/python-asyncssh/1.12.2-1ubuntu0.1