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

USN-5745-2: shadow regression

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Ubuntu Security Notice USN-5745-2
November 29, 2022

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

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

Summary:

USN-5745-1 introduced a regression in shadow.

Software Description:
- shadow: system login tools

Details:

USN-5745-1 fixed vulnerabilities in shadow. Unfortunately that update
introduced a regression that caused useradd to behave incorrectly in Ubuntu
14.04 ESM, Ubuntu 16.04 ESM, Ubuntu 18.04 LTS and Ubuntu 20.04 LTS. This
update reverts the security fix pending further investigation.

We apologize for the inconvenience.

Original advisory details:

Florian Weimer discovered that shadow was not properly copying and removing
user directory trees, which could lead to a race condition. A local attacker
could possibly use this issue to setup a symlink attack and alter or remove
directories without authorization.

Update instructions:

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

Ubuntu 20.04 LTS:
login 1:4.8.1-1ubuntu5.20.04.4
passwd 1:4.8.1-1ubuntu5.20.04.4
uidmap 1:4.8.1-1ubuntu5.20.04.4

Ubuntu 18.04 LTS:
login 1:4.5-1ubuntu2.5
passwd 1:4.5-1ubuntu2.5
uidmap 1:4.5-1ubuntu2.5

Ubuntu 16.04 ESM:
login 1:4.2-3.1ubuntu5.5+esm3
passwd 1:4.2-3.1ubuntu5.5+esm3
uidmap 1:4.2-3.1ubuntu5.5+esm3

Ubuntu 14.04 ESM:
login 1:4.1.5.1-1ubuntu9.5+esm3
passwd 1:4.1.5.1-1ubuntu9.5+esm3
uidmap 1:4.1.5.1-1ubuntu9.5+esm3

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

References:
https://ubuntu.com/security/notices/USN-5745-2
https://ubuntu.com/security/notices/USN-5745-1
https://launchpad.net/bugs/1998169

Package Information:
https://launchpad.net/ubuntu/+source/shadow/1:4.8.1-1ubuntu5.20.04.4
https://launchpad.net/ubuntu/+source/shadow/1:4.5-1ubuntu2.5