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Ubuntu Security Notice USN-6198-1
July 03, 2023

screen 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:

GNU Screen could be made to crash applications if it received specially
crafted input.

Software Description:
- screen: terminal multiplexer with VT100/ANSI terminal emulation

Details:

It was discovered that GNU Screen was not properly checking user
identifiers before sending certain signals to target processes. If GNU
Screen was installed as setuid or setgid, a local attacker could possibly
use this issue to cause a denial of service on a target application.

Update instructions:

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

Ubuntu 18.04 LTS (Available with Ubuntu Pro):
   screen                          4.6.2-1ubuntu1.1+esm1

Ubuntu 16.04 LTS (Available with Ubuntu Pro):
   screen                          4.3.1-2ubuntu0.1+esm1

Ubuntu 14.04 LTS (Available with Ubuntu Pro):
   screen 4.1.0~20120320gitdb59704-9ubuntu0.1~esm3

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

References:
   https://ubuntu.com/security/notices/USN-6198-1
   CVE-2023-24626