cis-gcp-cos-6.2.16

DevOps & Security

Ensure no duplicate UIDs exist

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6.2.16 Ensure no duplicate UIDs exist (Automated)

Description

Although the useradd program will not let you create a duplicate User ID (UID), it is possible for an administrator to manually edit the /etc/passwd file and change the UID field.

Rationale

Users must be assigned unique UIDs for accountability and to ensure appropriate access protections.

Audit Procedure

Run the following script and verify no results are returned:

#!/bin/bash

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

Expected Result

No results should be returned.

Remediation

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

Profile

Level 1 - Server