6.2.18 Ensure no duplicate user names exist (Scored) [SecScan]

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======6.2.18 Ensure no duplicate user names exist (Scored)======
=====Profile Applicability=====  
<code>
Level 1 - Server
Level 1 - Workstation 
</code>

=====Description=====
Although the ''useradd'' program will not let you create a duplicate user name, it is possible for an administrator to manually edit the ''/etc/passwd'' file and change the user name.

=====Rationale=====
If a user is assigned a duplicate user name, it will create and have access to files with the first UID for that username in ''/etc/passwd''. For example, if "test4" has a UID of 1000 and a subsequent "test4" entry has a UID of 2000, logging in as "test4" will use UID 1000. Effectively, the UID is shared, which is a security problem.

=====Audit===== 
Run the following script and verify no results are returned:
<Code:bash>
#!/bin/bash 
cat /etc/passwd | cut -f1 -d":" | sort -n | uniq -c | while read x ; do
  [ -z "${x}" ] && break 
  set - $x 
  if [ $1 -gt 1 ]; then 
    uids=`awk -F: '($1 == n) { print $3 }' n=$2 /etc/passwd | xargs` 
    echo "Duplicate User Name ($2): ${uids}" 
  fi 
done
</Code>

=====Remediation=====
Based on the results of the audit script, establish unique user names for the users. File ownerships will automatically reflect the change as long as the users have unique UIDs.