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CIS Ubuntu 14.04 LTS - 5.4.2 Ensure system accounts are non-login

DevOps & Security
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Verify system accounts have non-login shells and are locked to prevent interactive access

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5.4.2 Ensure system accounts are non-login (Scored)

Profile Applicability

  • Level 1 - Server
  • Level 1 - Workstation

Description

There are a number of accounts provided with Ubuntu that are used to manage applications and are not intended to provide an interactive shell.

Rationale

It is important to make sure that accounts that are not being used by regular users are prevented from being used to provide an interactive shell. By default, Ubuntu sets the password field for these accounts to an invalid string, but it is also recommended that the shell field in the password file be set to /usr/sbin/nologin. This prevents the account from potentially being used to run any commands.

Audit Procedure

Run the following script and verify no results are returned:

egrep -v "^\+" /etc/passwd | awk -F: '($1!="root" && $1!="sync" && $1!="shutdown" && $1!="halt" && $3<1000 && $7!="/usr/sbin/nologin" && $7!="/bin/false") {print}'

Expected Result

No output should be returned.

Remediation

Set the shell for any accounts returned by the audit script to /usr/sbin/nologin:

usermod -s /usr/sbin/nologin <user>

The following script will automatically set all user shells required to /usr/sbin/nologin and lock the sync, shutdown, and halt users:

#!/bin/bash

for user in `awk -F: '($3 < 1000) {print $1 }' /etc/passwd`; do
  if [ $user != "root" ]; then
    usermod -L $user
    if [ $user != "sync" ] && [ $user != "shutdown" ] && [ $user != "halt" ]; then
      usermod -s /usr/sbin/nologin $user
    fi
  fi
done

Default Value

System accounts have various shells by default.

References

  • CIS Controls: 16 - Account Monitoring and Control

Profile

  • Level 1 - Server
  • Level 1 - Workstation