Rules of Engagement (Network Vulnerability Assessments)

Rules of engagement govern the level and extent of vulnerability assessment efforts. Develop a written agreement between the audit manager and appropriate levels of senior management, as the vulnerability assessment process is extremely invasive. In this statement the questions of who, what, when, where, and how should be thoroughly, but briefly addressed. For example, the purpose of this vulnerability assessment will be to test the effectiveness of procedures ensuring that attackers cannot obtain unauthorized access to the organization's critical assets of human resources, data, and physical resources.

Assessment procedures define the methods and means by which the various evaluation events will take place. These procedures can be expressed in the following areas:

Assessment standing. Determine and define when the assessment will begin, the scope of the assessment, and when the assessment will end.

Vantage point. What will be the vantage point of the assessment? Should the auditors consider themselves as outside the organization, or inside the organization? Obviously, the vantage point will affect the assessment objectives and the time involved. In the insider vantage point, the auditors are provided as much pertinent information as possible. For example, auditors will have the source code for CGI scripts, network topology and architecture, IP addresses, etc. With this degree of information, the auditors may test the system more thoroughly looking for subtle flaws that might otherwise escape notice. Besides, this approach saves time and resources.

On the other hand, outsider testing provides little, if any, relevant system information to the auditors in the anticipation their stance is that of an outside attacker. This approach requires a great deal of time and effort to complete an accurate and meaningful assessment. Proponents of this type of assessment claim it provides a realistic approach to system evaluation in light of the fact outside attackers will not have insider information. The fact of the matter is with the large number of attacks attempting to gain access, or extinguish services, this approach requires a significant time investment, and it is likely that new vulnerabilities will be discovered before they can be tested against the system.

There are two more vulnerability modes, passive and aggressive. Passive testing means the auditor can take only a distant view, essentially a "looking glass" approach. This is a safe way of testing, but it is not going to provide the type of detail that should be narrated in the "findings" section of an audit report. The auditor discovers a system's vulnerability and reports findings without further exploration and system exploitation. Aggressive testing takes the approach of exploiting all discovered vulnerabilities and exploring just how far the auditor can penetrate the system before coming to an end.

How far should the auditor pursue an exploit? The answer should be explicitly detailed in the rules of engagement. However, it is recommended that the auditor pursue a vulnerability to the extent possible without doing damage to the system. Only in this fashion can the risk potential be measured and reported. It is further recommended that in a system vulnerability assessment, the procedure should be to locate a weakness, exploit it, and leverage that weakness to gain wider access to the target system