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.
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