Performing Authenticated Vulnerability Scan

Overview

Authenticated (credentialed) vulnerability scanning uses valid system credentials to log into target hosts and perform deep inspection of installed software, patches, configurations, and security settings. Compared to unauthenticated scanning, credentialed scans detect 45-60% more vulnerabilities with significantly fewer false positives because they can directly query installed packages, registry keys, and file system contents.

When to Use

• When conducting security assessments that involve performing authenticated vulnerability scan
• When following incident response procedures for related security events
• When performing scheduled security testing or auditing activities
• When validating security controls through hands-on testing

Prerequisites

• Vulnerability scanner (Nessus, Qualys, OpenVAS, Rapid7 InsightVM)
• Service accounts with appropriate privileges on target systems
• Secure credential storage (vault integration preferred)
• Network access from scanner to target management ports
• Written authorization from system owners

Core Concepts

Why Authenticated Scanning

Unauthenticated scanning can only assess externally visible services and banners, often leading to:

• Missed vulnerabilities in locally installed software
• Inaccurate version detection from banner changes
• Inability to check patch levels, configurations, or local policies
• Higher false positive rates due to inference-based detection

Authenticated scanning resolves these by directly querying the target OS.

Credential Types by Platform

Linux/Unix Systems

• SSH Key Authentication: RSA/Ed25519 key pairs (recommended)
• SSH Username/Password: Fallback for systems without key-based auth
• Sudo/Su Elevation: Non-root user with sudo privileges
• Certificate-based SSH: X.509 certificates for enterprise environments

Windows Systems

• SMB (Windows): Domain or local admin credentials
• WMI: Windows Management Instrumentation queries
• WinRM: Windows Remote Management (HTTPS preferred)
• Kerberos: Domain authentication with service tickets

Network Devices

• SNMP v3: USM with authentication and privacy (AES-256)
• SSH: For Cisco IOS, Juniper JunOS, Palo Alto PAN-OS
• API Tokens: REST API for modern network platforms

Databases

• Oracle: SYS/SYSDBA credentials or TNS connection
• Microsoft SQL Server: Windows auth or SQL auth
• PostgreSQL: Role-based authentication
• MySQL: User/password with SELECT privileges

Workflow

Step 1: Create Dedicated Service Accounts

# Linux: Create scan service account
sudo useradd -m -s /bin/bash -c "Vulnerability Scanner Service Account" nessus_svc
sudo usermod -aG sudo nessus_svc

# Configure sudo for passwordless specific commands
echo 'nessus_svc ALL=(ALL) NOPASSWD: /usr/bin/dpkg -l, /usr/bin/rpm -qa, \
/bin/cat /etc/shadow, /usr/sbin/dmidecode, /usr/bin/find' | sudo tee /etc/sudoers.d/nessus_svc

# Generate SSH key pair
sudo -u nessus_svc ssh-keygen -t ed25519 -f /home/nessus_svc/.ssh/id_ed25519 -N ""

# Distribute public key to targets
for host in $(cat target_hosts.txt); do
    ssh-copy-id -i /home/nessus_svc/.ssh/id_ed25519.pub nessus_svc@$host
done

# Windows: Create scan service account via PowerShell
New-ADUser -Name "SVC_VulnScan" `
    -SamAccountName "SVC_VulnScan" `
    -UserPrincipalName "SVC_VulnScan@domain.local" `
    -Description "Vulnerability Scanner Service Account" `
    -PasswordNeverExpires $true `
    -CannotChangePassword $true `
    -Enabled $true `
    -AccountPassword (Read-Host -AsSecureString "Enter Password")

# Add to local Administrators group on targets via GPO or:
Add-ADGroupMember -Identity "Domain Admins" -Members "SVC_VulnScan"
# For least privilege, use a dedicated GPO for local admin rights instead

# Enable WinRM on targets
Enable-PSRemoting -Force
Set-Item WSMan:\localhost\Service\AllowRemote -Value $true
winrm set winrm/config/service '@{AllowUnencrypted="false"}'

Step 2: Configure Scanner Credentials

Nessus Configuration

{
  "credentials": {
    "add": {
      "Host": {
        "SSH": [{
          "auth_method": "public key",
          "username": "nessus_svc",
          "private_key": "/path/to/id_ed25519",
          "elevate_privileges_with": "sudo",
          "escalation_account": "root"
        }],
        "Windows": [{
          "auth_method": "Password",

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