Introduction to the Open Source Security Testing Methodology (OSSTM)

Penetration testing, also known as ethical hacking, is an authorized cybersecurity practice aimed at proactively identifying vulnerabilities in IT systems, networks, and applications. Among the various pen testing methodologies, the Open Source Security Testing Methodology (OSSTM) stands out as a widely used and proven approach.

What is OSSTM?

OSSTM is an open source and flexible penetration testing methodology designed to improve cybersecurity. It provides guidelines for systematically testing IT environments for security weaknesses through proven penetration testing techniques and tools.

OSSTM was created in 2009 by Pete Herzog and is maintained by the non-profit Institute for Security and Open Methodologies (ISECOM). It is offered under an open source license for anyone to use or contribute to.

The methodology outlines key testing principles, activities, outputs, and resources that testers can adapt for their specific needs. By providing a structured framework, OSSTM allows for consistency, thoroughness, and transparency in execution.

Objectives of OSSTM

The core objectives of the OSSTM methodology include:

  • Identifying vulnerabilities and weaknesses across networks, systems, and applications that could be exploited by threat actors.
  • Assessing the effectiveness of existing cybersecurity controls and measures.
  • Quantifying cyber risks faced by an organization based on testing insights.
  • Providing actionable recommendations for enhancing defenses and fixing security gaps.
  • Improving overall security posture through proactive improvements.
  • Meeting legal and regulatory compliance requirements related to cybersecurity.
  • Enabling informed decision-making for IT and cybersecurity planning and investment.

OSSTM Principles

OSSTM is based on several guiding principles and concepts that penetration testers must adhere to:

  • Ethical hacking – Mimic real-world attacks but in a legal and ethical way. Obtain proper permission and scope.
  • Four Ds – Discover vulnerabilities, Document findings, Diagnose risks, and Deliver results.
  • Risk-based approach – Prioritize testing based on probability and business impact of threats.
  • Applied knowledge – Leverage experience, creativity, and intuition in combination with proven techniques.
  • Methodical process – Follow a structured approach but adapt to situations as required.
  • Customizable – Flexibility to tailor testing for specific environments and objectives.
  • Transparency – Maintain visibility through detailed scoping and reporting.
  • Insight over exploits – Focus on gathering insights rather than just exploiting flaws.

OSSTM – Key Testing Processes

The OSSTM framework divides penetration testing into several phases encompassing information gathering, planning, discovery, attack, analysis, and reporting.

Some key activities under each testing stage include:

  • Pre-engagement Interactions – Requirements gathering, defining testing scope and boundaries, scheduling, contracting.
  • Information Gathering – Passively gathering data about the target infrastructure through search engines, social media, public databases.
  • Threat Modeling – Outlining important assets, possible threats, exploitable vulnerabilities, and estimating risk levels.
  • Vulnerability Analysis – Leveraging vulnerability scanning tools like Nessus to identify known weaknesses in target systems.
  • Discovery – Enumerating target infrastructure through techniques like port scanning, service detection, OS fingerprinting, etc.
  • Attack Surface Mapping – Finding potential entry points where systems can be probed and penetrated.
  • Exploitation – Attempting to penetrate identified vulnerabilities using techniques like password cracking, SQL injection, XSS attacks, etc.
  • Post Exploitation – After gaining access, performing lateral movement throughout systems and maintaining persistence.
  • Reporting – Documenting findings in detail with risk ratings, steps to replicate, remediation advice, etc.

Benefits of the OSSTM Methodology

OSSTM offers several advantages that make it one of the most widely accepted penetration testing methodologies globally:

  • Structured and methodical approach following best practices.
  • Promotes consistency and completeness in testing.
  • Highly transparent methodology.
  • Designed for maximum flexibility and customization.
  • Vendor neutral – can be applied to diverse environments.
  • Open source and community-driven methodology.
  • Global community support and continuous improvements.
  • Reduces reliance on individual skills through standardized processes.
  • Ideal for novice pen testers as well as experienced professionals.


As systems get more complex and the threat landscape evolves, continuous security testing becomes critical. OSSTM provides an excellent open source framework for methodical and effective penetration testing tailored to organizational needs.

By revealing vulnerabilities proactively, OSSTM allows organizations to enhance security defenses before hackers and cybercriminals attempt exploitation. With its flexibility and transparency, it is one of the most trusted penetration testing methodologies for strengthening enterprise security.