5.1.3 Ensure group names and GIDs are unique

Information

All groups should have a unique GID on the system.

All groups should have an individual and unique GID. If GID numbers are shared this could lead to undesirable file and directory access.

Solution

- Examine the

group IDs

(GID) of all locally configured accounts:

cut -d: -f 3 /etc/group |sort -n | uniq -d

If the command has output there is at least one duplicate GID number. Determine any duplicates within the /etc/group file:

cut -d: -f 1 /etc/group | sort -n | uniq -d | while read GID; do
cut -f "1 3 4" -d : /etc/group | /usr/bin/sort -t: -k2n | grep ":${GID}:"
done
- Examine the

names

of all locally configured groups:

cut -d: -f 1 /etc/group |sort -n | uniq -d

If the command has output there is at least one duplicate group name. Determine any duplicates within the /etc/group file:

cut -d: -f 1 /etc/passwd | sort -n | uniq -d | while read groupname; do
cut -f "1 3 4" -d : /etc/group | /usr/bin/sort -t: -k2n | grep "${groupname}:"
done

NOTE : Any duplicates returned should either be deleted or have the GID changed. Be careful. We recommend you examine any accounts assigned to a duplicate and ensure the account is neither losing nor gaining authorized group access through any remedial action.

To remove:

rmgroup <groupname>

To change the UID:

chgroup id=<id> <groupname>

See Also

https://workbench.cisecurity.org/benchmarks/10385

Item Details

Category: ACCESS CONTROL

References: 800-53|AC-2, CSCv7|16.6

Plugin: Unix

Control ID: 2cd20bb86b31e3ba3518597e219cf7cfc1b7acdd1ae5ac6edee5a629d7333d8c