Description
UsePAM Enables the Pluggable Authentication Module interface. If set to “yes” this will
enable PAM authentication using ChallengeResponseAuthentication and
PasswordAuthentication in addition to PAM account and session module processing for all
authentication types.
To enable PAM authentication, add or correct the following line in
/etc/ssh/sshd_config:
Rationale
When UsePAM is set to yes, PAM runs through account and session types properly. This is
important if you want to restrict access to services based off of IP, time or other factors of
the account. Additionally, you can make sure users inherit certain environment variables
on login or disallow access to the server.
Shell script
The following script can be run on the host to remediate the issue.
# Remediation is applicable only in certain platforms
if [ ! -f /.dockerenv ] && [ ! -f /run/.containerenv ]; then
if [ -e "/etc/ssh/sshd\_config" ] ; then
LC\_ALL=C sed -i "/^\s\*UsePAM\s\+/Id" "/etc/ssh/sshd\_config"
else
touch "/etc/ssh/sshd\_config"
fi
# make sure file has newline at the end
sed -i -e '$a\' "/etc/ssh/sshd\_config"
cp "/etc/ssh/sshd\_config" "/etc/ssh/sshd\_config.bak"
# Insert before the line matching the regex '^Match'.
line\_number="$(LC\_ALL=C grep -n "^Match" "/etc/ssh/sshd\_config.bak" | LC\_ALL=C sed 's/:.\*//g')"
if [ -z "$line\_number" ]; then
# There was no match of '^Match', insert at
# the end of the file.
printf '%s\n' "UsePAM yes" >> "/etc/ssh/sshd\_config"
else
head -n "$(( line\_number - 1 ))" "/etc/ssh/sshd\_config.bak" > "/etc/ssh/sshd\_config"
printf '%s\n' "UsePAM yes" >> "/etc/ssh/sshd\_config"
tail -n "+$(( line\_number ))" "/etc/ssh/sshd\_config.bak" >> "/etc/ssh/sshd\_config"
fi
# Clean up after ourselves.
rm "/etc/ssh/sshd\_config.bak"
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: Enable PAM
block:
- name: Check for duplicate values
lineinfile:
path: /etc/ssh/sshd\_config
create: false
regexp: (?i)^\s\*UsePAM\s+
state: absent
check\_mode: true
changed\_when: false
register: dupes
- name: Deduplicate values from /etc/ssh/sshd\_config
lineinfile:
path: /etc/ssh/sshd\_config
create: false
regexp: (?i)^\s\*UsePAM\s+
state: absent
when: dupes.found is defined and dupes.found > 1
- name: Insert correct line to /etc/ssh/sshd\_config
lineinfile:
path: /etc/ssh/sshd\_config
create: true
regexp: (?i)^\s\*UsePAM\s+
line: UsePAM yes
state: present
insertbefore: ^[#\s]\*Match
validate: /usr/sbin/sshd -t -f %s
when: ansible\_virtualization\_type not in ["docker", "lxc", "openvz", "podman", "container"]
tags:
- DISA-STIG-UBTU-20-010035
- PCI-DSSv4-2.2.4
- low\_complexity
- low\_disruption
- medium\_severity
- no\_reboot\_needed
- restrict\_strategy
- sshd\_enable\_pam
