A tmux security update has been released for Ubuntu Linux 20.04 LTS and 20.10.

USN-4618-1: tmux vulnerability

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Ubuntu Security Notice USN-4618-1
November 05, 2020

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

- Ubuntu 20.10
- Ubuntu 20.04 LTS

Summary:

tmux could be made to crash or execute arbitrary code if it received
a specially crafted input.

Software Description:
- tmux: terminal multiplexer

Details:

Sergey Nizovtsev discovered that tmux incorrectly handled some inputs.
An attacker could possibly use this issue to cause a crash or execute arbitrary code.

Update instructions:

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

Ubuntu 20.10:
tmux 3.1b-1ubuntu0.1

Ubuntu 20.04 LTS:
tmux 3.0a-2ubuntu0.2

After a standard system update you need to restart tmux session to make
all the necessary changes.

References:
  https://usn.ubuntu.com/4618-1
CVE-2020-27347

Package Information:
  https://launchpad.net/ubuntu/+source/tmux/3.1b-1ubuntu0.1
  https://launchpad.net/ubuntu/+source/tmux/3.0a-2ubuntu0.2