Understanding Threat Categories

While there are many variations of specific attacks and attack techniques, it is useful to think about threats in terms of what the attacker is trying to achieve. This changes your focus from the identification of every specific attack ” which is really just a means to an end ” to focusing on the end results of possible attacks.

STRIDE

Threats faced by the application can be categorized based on the goals and purposes of the attacks. A working knowledge of these categories of threats can help you organize a security strategy so that you have planned responses to threats. STRIDE is the acronym used at Microsoft to categorize different threat types. STRIDE stands for:

• Spoofing . Spoofing is attempting to gain access to a system by using a false identity. This can be accomplished using stolen user credentials or a false IP address. After the attacker successfully gains access as a legitimate user or host, elevation of privileges or abuse using authorization can begin.

• Tampering . Tampering is the unauthorized modification of data, for example as it flows over a network between two computers.

• Repudiation . Repudiation is the ability of users (legitimate or otherwise ) to deny that they performed specific actions or transactions. Without adequate auditing, repudiation attacks are difficult to prove .

• Information disclosure . Information disclosure is the unwanted exposure of private data. For example, a user views the contents of a table or file he or she is not authorized to open , or monitors data passed in plaintext over a network. Some examples of information disclosure vulnerabilities include the use of hidden form fields, comments embedded in Web pages that contain database connection strings and connection details, and weak exception handling that can lead to internal system level details being revealed to the client. Any of this information can be very useful to the attacker.

• Denial of service . Denial of service is the process of making a system or application unavailable. For example, a denial of service attack might be accomplished by bombarding a server with requests to consume all available system resources or by passing it malformed input data that can crash an application process.

• Elevation of privilege . Elevation of privilege occurs when a user with limited privileges assumes the identity of a privileged user to gain privileged access to an application. For example, an attacker with limited privileges might elevate his or her privilege level to compromise and take control of a highly privileged and trusted process or account.

STRIDE Threats and Countermeasures

Each threat category described by STRIDE has a corresponding set of countermeasure techniques that should be used to reduce risk. These are summarized in Table 2.1. The appropriate countermeasure depends upon the specific attack. More threats, attacks, and countermeasures that apply at the network, host, and application levels are presented later in this chapter.

Table 2.1: STRIDE Threats and Countermeasures

Threat	Countermeasures
Spoofing user identity	Use strong authentication. Do not store secrets (for example, passwords) in plaintext. Do not pass credentials in plaintext over the wire. Protect authentication cookies with Secure Sockets Layer (SSL).
Tampering with data	Use data hashing and signing. Use digital signatures. Use strong authorization. Use tamper-resistant protocols across communication links. Secure communication links with protocols that provide message integrity.
Repudiation	Create secure audit trails. Use digital signatures.
Information disclosure	Use strong authorization. Use strong encryption. Secure communication links with protocols that provide message confidentiality. Do not store secrets (for example, passwords) in plaintext.
Denial of service	Use resource and bandwidth throttling techniques. Validate and filter input.
Elevation of privilege	Follow the principle of least privilege and use least privileged service accounts to run processes and access resources.