# Vulnerability Assessment of Sensor Systems
## 4 Validation of the Sensor System Vulnerability Assessment Method
Case 2: Search of Public Domain Sources to Identify Potential Vulnerabilities in the TOE (AVA_VANx.2E, x = 1,2,3,4)  
Case 2 is very complex and extensive because IT products may have diversified hardware- and software-specific vulnerabilities and public information sources are numerous and diversified. For this reason, it is divided into two issues:  
* search planning--performed by \"EEP2-1 Identification of Vulnerability-related issues\",
* search execution--performed by \"EEP2-2 Search of public domain sources to identify potential vulnerabilities and attacks\". EEP2-1 identifies keywords describing the TOE, e.g., the MEDIS sensor, as precisely as possible:  
1. The evaluator reviews the TOE characteristics included in the Security Target (mainly its introduction), such as TOE type, description, and overview, and identifies adequate keywords, attributes, or statements for the future search for potential vulnerabilities. More details of the MEDIS example can be found in Section 4.1[37]. 2. The evaluator looks for differences and similarities to earlier evaluated products, reviewing a knowledge base in the CC portal [6], with the use of the general _CCtaxonomy_. These categories may also serve as keywords. 3. All keywords, attributes, or statements which best characterize the evaluated IT product are placed into the _VulRelatIssue_VRI_ knowledge base. The EEP2-1 input is:  
* the security target of the evaluated product, especially \"ST Introduction\" with the above-mentioned TOE characteristics,
* the CC portal [6]--a knowledge base including the simplified ST and ETR of the evaluated products, grouped according to _CCtaxonomy_: access control devices and systems, biometric systems and devices, boundary protection devices and systems, data protection, databases, etc. The EEP2-1 output is:  
* the _VulRelatIssue_VRI_ knowledge base (keywords, attributes, or statements precisely characterizing the TOE, defining the range of the planned searching). Figure 2 presents an ontological model example concerning vulnerability-related issues. The left panel shows the class hierarchy of the CCO ontology (CCO-2019-01-07.owl is available on the Supplementary Materials) described in the author's earlier papers. The _VulRelatIssue_VRI_ class has two individuals shown in the middle panel--one for the MyFWL_1 firewall and one for the MEDIS sensor. For the highlighted _VRI_MEDIS_ individual, the object and data properties expressing the related knowledge are shown in the right panel. Please note that the _VulRelatIssue-VRI_ knowledge base expresses \"what to search\". The keywords (data properties) used while the sources are searched are:  
* TOE-related keywords derived from the security target parts:
* TOE_typekeywords_--defined on a \"TOE type\" basis,
* TOE_usageSecFeature_Keywords_--defined on the basis of an ST section entitled \"usage and major security features of a TOE\",
* TOE_operEnv_Keywords_--defined on the basis of an ST section entitled \"required non-TOE hardware, software, firmware\",
* targetEnv_Hardware_--hardware platform, e.g., a microcontroller,
* targetEnv_Software_--software platform, e.g., OS,
* keywords implied by the CC product taxonomy,
* keywords for IT products knowledge bases,
* CPE_keywords_--according to [45], if relevant,
* genIT_Product_Keywords_--other than those defined by the evaluator, concerning the TOE application, operational environment, specific threats, etc.,
* similar_Products_--indicating similar IT products. The main activities related to Case 2 concern the \"EEP2-2 search of public domain sources to identify potential vulnerabilities and attacks\" process. The author proposes to develop the _InfoSourceTaxonomy_ knowledge base, allowing one to access the knowledge dealing with the potential vulnerabilities and attacks. This way, the evaluators have access to public information sources relevant for the IT products  
Figure 2: The vulnerability-related issues represented by the ontological model in the Protege  
usually evaluated by ITSEF.