Understanding Vulnerability Scan Types: Agent, Agentless, Authenticated, and Unauthenticated Explained
December 16th, 2025
Understanding Security Scanning Approaches and Related Techniques
Modern security programs rely on multiple assessment techniques to identify vulnerabilities, misconfigurations, and unknown assets. These techniques differ in how they collect data, what level of access they require, and where they operate within the network. Understanding these distinctions helps security teams choose the right approach for their environment and risk tolerance.
Agent-Based Scanning
Agent-based scanning relies on lightweight software installed directly on host systems like endpoints, workstations, and servers. Agent-based runs locally with direct access to the operating system, collects detailed system level data, and operates either continuously or on a scheduled basis. Agent-based scanning’s advantages include high visibility into system configuration and state and being less dependent on network accessibility (firewalls can block scans by agentless software). Agent-based scanning may not be suitable for organizations that do not want to regularly install and maintain scanning software or to take on the associated performance overhead on their host systems.
Typical Use Cases:
Endpoint security monitoring
Configuration compliance validation
Continuous vulnerability assessment
Circumventing network accessibility controls
Agentless Scanning
Agentless scanning collects information remotely over the network using standard protocols and interfaces. Agentless scanning does not require the installation or maintenance of software on individual systems and is able to quickly scale across large environments. Agentless scanning uses network-based discovery and interrogation for network-wide vulnerability scanning. Compared to agent-based scanning, agentless scanning is easier to deploy and more suitable for asset discovery, but lags behind agent-based scanning in terms of visibility and being dependent on network accessibility and permissions.
Typical Use Cases:
Asset discovery
Network-wide vulnerability scanning
External and perimeter assessments
Authenticated (Credentialed) Scanning
Authenticated scanning involves using valid credentials to log into systems and view configuration software details directly. This type of scanning accesses system/network internals such as patch levels and registry settings using OS-native interfaces like SSH and APIs. Authenticated scanning has advantages like high accuracy, fewer false positives, strong visibility, and being effective for system hardening initiatives. Organizations who perform authenticated scans must practice secure credential management for scanning tools due to the increased risk and impact of credentials being compromised.
Typical Use Cases
Configuration baseline validation
Patch management verification
Security compliance assessments
Non-Authenticated (Non-Credentialed) Scanning
Non-authenticated scanning examines systems without logging in, relying on the responses of exposed services. Non-authenticated scans mimic an external attacker’s perspective and interact with open ports and network services. Non-authenticated scans carry a lower operational risk than authenticated scans and are particularly useful for external attack surface analysis. Non-authenticated scans do have a higher likelihood of generating false positives and, naturally, offer less visibility than authenticated scans.
Typical Use Cases
External vulnerability scanning
Perimeter security testing
Baseline exposure assessment
Final thoughts
Effective security scanning is not a one-size-fits-all process, but rather a layered approach that balances visibility, scalability, and risk. Agent-based and authenticated scans provide deep, accurate insight into system configurations and vulnerabilities, while agentless and non-authenticated scans offer broad coverage and an attacker’s-eye view of the environment. By understanding the strengths and limitations of each scanning method, organizations can combine these techniques strategically to improve asset visibility, reduce risk, and build a more resilient security posture aligned with their operational and risk management goals.
— Ben Skinner