nuclei-templates/code/linux/audit/ssh-gssapiauthentication-disabled.yaml

id: ssh-gssapiauthentication-disabled

info:
  name: sshd GSSAPIAuthentication - Disabled
  author: Th3l0newolf
  severity: low
  description: |
    The GSSAPIAuthentication parameter in the SSH configuration file (sshd_config) controls whether GSSAPI-based user authentication is permitted. When enabled, it allows the use of Kerberos or other GSSAPI mechanisms for authenticating SSH connections.
  remediation:
    Disable GSSAPIAuthentication by editing /etc/ssh/sshd_config to set GSSAPIAuthentication no and restart SSH with sudo systemctl restart sshd.
  reference:
    - https://www.cisecurity.org/benchmark/ubuntu_linux
  metadata:
    verified: true
  tags: cis,local,ssh,linux,audit,ubuntu,benchmark

self-contained: true

code:
  - engine:
      - bash

    args:
      - "-c"

      - |
        # Use sudo for elevated access to parse the effective SSH configuration
        if ! command -v sshd &> /dev/null; then
          echo "[cis-ssh-gssapiauthentication-disabled:Policy-Error] [SSH daemon not found] [CIS_ERROR] [medium]"
          exit 1
        fi

        # Get the effective SSH configuration
        if ! gssapi_auth=$(sudo sshd -T 2>/dev/null | grep -i gssapiauthentication | awk '{print tolower($2)}' | tr -d ' \t'); then
          echo "[cis-ssh-gssapiauthentication-disabled:Policy-Error] [Failed to get SSH configuration] [CIS_ERROR] [medium]"
          exit 1
        fi

        # Check if the value is explicitly set to 'no'
        if [[ -n "$gssapi_auth" && "$gssapi_auth" == "no" ]]; then
          echo "[cis-ssh-gssapiauthentication-disabled:Policy-Pass] [GSSAPIAuthentication $gssapi_auth] [CIS_PASS] [medium]"
        else
          echo "[cis-ssh-gssapiauthentication-disabled:Policy-Fail] [GSSAPIAuthentication ${gssapi_auth:-unset}] [CIS_FAIL] [medium]"
        fi

    matchers:
      - type: word
        name: policy-pass
        words:
          - "Policy-Pass"

      - type: word
        name: policy-fail
        words:
          - "Policy-Fail"

      - type: word
        name: policy-error
        words:
          - "Policy-Error"
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