Enforce Usage of pam_wheel with Group Parameter for su Authentication
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Description
To ensure that only users who are members of the group set in the group
option of
pam_wheel.so
module can run commands with altered privileges through the su
command, make sure that the following line exists in the file /etc/pam.d/su
:
auth required pam_wheel.so use_uid group=sugroup
Rationale
The su
program allows to run commands with a substitute user and group ID.
It is commonly used to run commands as the root user.
Limiting access to such command is considered a good security practice.
Shell script
The following script can be run on the host to remediate the issue.
#!/bin/bash
# Remediation is applicable only in certain platforms
if dpkg-query --show --showformat='${db:Status-Status}\n' 'libpam-runtime' 2>/dev/null | grep -q installed; then
var_pam_wheel_group_for_su='sugroup'
PAM_CONF=/etc/pam.d/su
pamstr=$(grep -P '^auth\s+required\s+pam_wheel\.so\s+(?=[^#]*\buse_uid\b)(?=[^#]*\bgroup=)' ${PAM_CONF})
if [ -z "$pamstr" ]; then
sed -Ei '/^auth\b.*\brequired\b.*\bpam_wheel\.so/d' ${PAM_CONF} # remove any remaining uncommented pam_wheel.so line
sed -Ei "/^auth\s+sufficient\s+pam_rootok\.so.*$/a auth required pam_wheel.so use_uid group=${var_pam_wheel_group_for_su}" ${PAM_CONF}
else
group_val=$(echo -n "$pamstr" | grep -Eo '\bgroup=[_a-z][-0-9_a-z]*' | cut -d '=' -f 2)
if [ -z "${group_val}" ] || [ ${group_val} != ${var_pam_wheel_group_for_su} ]; then
sed -Ei "s/(^auth\s+required\s+pam_wheel.so\s+[^#]*group=)[_a-z][-0-9_a-z]*/\1${var_pam_wheel_group_for_su}/" ${PAM_CONF}
fi
fi
else
>&2 echo 'Remediation is not applicable, nothing was done'
fi
Ansible playbook
The following playbook can be run with Ansible to remediate the issue.
- name: Gather the package facts
package_facts:
manager: auto
tags:
- PCI-DSSv4-2.2
- PCI-DSSv4-2.2.6
- low_complexity
- low_disruption
- medium_severity
- no_reboot_needed
- restrict_strategy
- use_pam_wheel_group_for_su
- name: XCCDF Value var_pam_wheel_group_for_su # promote to variable
set_fact:
var_pam_wheel_group_for_su: !!str sugroup
tags:
- always
- name: Enforce Usage of pam_wheel with Group Parameter for su Authentication - Add
the group to the /etc/pam.d/su file
ansible.builtin.lineinfile:
path: /etc/pam.d/su
state: present
regexp: ^[\s]*#[\s]*auth[\s]+required[\s]+pam_wheel\.so[\s]+use_uid group=$
line: auth required pam_wheel.so use_uid group={{ var_pam_wheel_group_for_su
}}
when: '"libpam-runtime" in ansible_facts.packages'
tags:
- PCI-DSSv4-2.2
- PCI-DSSv4-2.2.6
- low_complexity
- low_disruption
- medium_severity
- no_reboot_needed
- restrict_strategy
- use_pam_wheel_group_for_su
Warning
Note that ensure_pam_wheel_group_empty
rule complements this requirement by
ensuring the referenced group exists and has no members.