Enable GSSAPI Authentication

An XCCDF Rule

Description

Sites setup to use Kerberos or other GSSAPI Authenticaion require setting sshd to accept this authentication. To enable GSSAPI authentication, add or correct the following line in /etc/ssh/sshd_config:

GSSAPIAuthentication yes

Rationale

Kerberos authentication for SSH is often implemented using GSSAPI. If Kerberos is enabled through SSH, the SSH daemon provides a means of access to the system's Kerberos implementation. Vulnerabilities in the system's Kerberos implementations may be subject to exploitation. For enterprises, Kerberos is often enabled and used with GSSAPI for centralized user account management which may necessitate enabling of GSSAPI functionality in SSH.

ID: xccdf_org.ssgproject.content_rule_sshd_enable_gssapi_auth
Severity: Medium
Updated: about 1 year ago

# 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*GSSAPIAuthentication\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 at the beginning of the file
printf '%s\n' "GSSAPIAuthentication yes" > "/etc/ssh/sshd_config"
cat "/etc/ssh/sshd_config.bak" >> "/etc/ssh/sshd_config"
# Clean up after ourselves.
rm "/etc/ssh/sshd_config.bak"

else
    >&2 echo 'Remediation is not applicable, nothing was done'
fi

- name: Enable GSSAPI Authentication
  block:

  - name: Check for duplicate values
    lineinfile:
      path: /etc/ssh/sshd_config      create: true
      regexp: (?i)^\s*GSSAPIAuthentication\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: true
      regexp: (?i)^\s*GSSAPIAuthentication\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*GSSAPIAuthentication\s+
      line: GSSAPIAuthentication yes
      state: present
      insertbefore: BOF
      validate: /usr/sbin/sshd -t -f %s
  when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy
  - sshd_enable_gssapi_auth

Enable GSSAPI Authentication

Description

Rationale

Remediation - Shell Script

Remediation - Ansible