CIS Ubuntu 14.04 LTS - 6.2.17 Ensure no duplicate GIDs exist

6.2.17 Ensure no duplicate GIDs exist (Scored)

Profile Applicability

• Level 1 - Server
• Level 1 - Workstation

Description

Although the groupadd program will not let you create a duplicate Group ID (GID), it is possible for an administrator to manually edit the /etc/group file and change the GID field.

Rationale

User groups must be assigned unique GIDs for accountability and to ensure appropriate access protections.

Audit Procedure

Run the following script and verify no results are returned:

#!/bin/bash

cat /etc/group | cut -f3 -d":" | sort -n | uniq -c | while read x ; do
  [ -z "${x}" ] && break
  set - $x
  if [ $1 -gt 1 ]; then
    groups=`awk -F: '($3 == n) { print $1 }' n=$2 /etc/group | xargs`
    echo "Duplicate GID ($2): ${groups}"
  fi
done

Expected Result

No output should be returned.

Remediation

Based on the results of the audit script, establish unique GIDs and review all files owned by the shared GID to determine which group they are supposed to belong to.

Default Value

Not applicable.

Notes

You can also use the grpck command to check for other inconsistencies in the /etc/group file.

References

None

CIS Controls

16 Account Monitoring and Control - Account Monitoring and Control

Profile

• Level 1