When performing Threat Modeling during code review, it is important to follow a structured process. The goal is to identify, evaluate, and reduce the security risks associated with an application.

This process can be broken down into three main phases:

1. Application Decomposition

The first step consists of understanding the application and its interactions with external entities. This involves creating use cases to analyze how the application is used, identifying entry points where a potential attacker could interact with the application, pinpointing assets that might be of interest to an attacker, and defining trust levels, which represent the access rights granted to external entities. This information is documented in a threat model, which also includes Data Flow Diagrams (DFDs) that show data paths through the system, highlighting privilege boundaries.

2. Threat Identification and Classification

Once the application has been decomposed, the next step is to determine and classify the threats. This process requires the use of a threat categorization methodology, such as the STRIDE model, which helps to systematically identify threats based on common attacker goals, such as spoofing, tampering, denial of service, and so on. Each identified threat is further analyzed to understand its potential impact and the ease with which it can be exploited, allowing for the creation of a prioritized list of threats to mitigate.

3. Countermeasures and Mitigation

After identifying the threats, it is essential to determine the countermeasures to implement to mitigate the associated risks. Countermeasures can include security controls, changes to the application design, or even the removal of features that present risks that are too high. In some cases, it might be acceptable to accept a risk if the countermeasures are too expensive or complex to implement, provided that the risk is documented and managed appropriately.

Threat Modeling allows for addressing the most critical threats effectively, minimizing application vulnerabilities and improving its overall security.

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