Security Properties

The CIA triad identifies three primary security properties:

• Confidentiality restricts access to information so that only authorized people and processes can view it.

• Integrity ensures that data and systems remain accurate and that only authorized parties can change them.

• Availability ensures that systems and data remain usable when needed.

Confidentiality and Related Concepts

Privacy, anonymity, and secrecy are related to confidentiality, but each has a different focus:

• Privacy governs how personal information is collected, used, stored, and shared.

• Anonymity separates an identity from an observable action.

• Secrecy deliberately conceals information and may conceal its existence.

Integrity

Integrity applies to data, its source, and the system processing it:

• Data integrity protects information against unauthorized modification or deletion.

• Origin integrity protects the connection between information and its asserted source.

• System integrity provides confidence that hardware, software, and processes continue to operate as intended.

Authenticity and Accountability

Authenticity provides evidence that a person, system, or message is genuine. Integrity asks whether something changed. Authenticity asks whether its claimed source is genuine.

Accountability connects actions to the people or systems responsible for them.

Availability and Denial of Service

A denial-of-service (DoS) attack targets availability by making a system unavailable or too slow to be useful. A distributed denial-of-service (DDoS) attack sends traffic or requests from many systems at once.

Security System Goals

Security controls support three operational goals:

1. Prevention attempts to stop an attack or failure before it succeeds.

2. Detection identifies and reports attacks, attempted attacks, and unexpected behavior.

3. Recovery restores systems and operations after an attack or failure.

No one goal replaces the others. Prevention can fail, detection does not repair damage, and recovery is harder when an incident was never detected.

Defense in depth uses several independent layers of protection so that the failure of one control does not compromise the entire system. The layers may prevent, detect, limit, or help recover from the same event.

Policies, Mechanisms, and Assurance

Securing a system requires two separate decisions: what is allowed and how that decision is enforced.

• A policy defines which actions are allowed.

• A mechanism enforces a policy.

Mechanisms fall into two groups:

• Technical mechanisms use hardware or software to enforce a policy, including access controls, cryptography, and intrusion detection.

• Procedural mechanisms rely on people following a defined process, including identity checks, audits, and separation of duties.

Every mechanism depends on assumptions about the system and its environment. When an assumption is wrong, the mechanism may stop enforcing its policy without an obvious sign of failure.

Assurance measures the confidence that a system correctly enforces its policies. That confidence comes from evidence gathered through design reviews, testing, code audits, and penetration testing.

Security engineering applies these ideas throughout a system’s design, implementation, and operation. It treats security as an ongoing engineering problem involving cost, usability, evolving threats, and recovery.

The Trusted Computing Base (TCB) contains the hardware, firmware, and software that must work correctly for the system’s security rules to hold. A trust boundary is a point where data or control passes between parts of a system that are trusted differently.

The supply chain includes the people, tools, vendors, and components used to build and deliver a system. Supply chain security protects that process, including software dependencies, build systems, and update channels.

Security theater describes a measure that creates the appearance of protection without meaningfully reducing risk. Misaligned incentives arise when the party deciding how much security to buy does not bear the full cost of failure.

Risk Analysis

Risk analysis identifies what needs to be protected, determines how it could be harmed, assesses the likelihood and impact of that harm, and prioritizes ways to address the risk. The sequence is:

asset -> threat -> vulnerability -> attack vector -> security control -> residual risk

Each term in the sequence has a specific role:

• An asset is something valuable that must be protected.

• A threat is a circumstance or event with the potential to cause harm.

• A vulnerability is a weakness that could allow a security property to fail.

• An attack vector is the path or method used to gain access or produce an effect.

• A security control, or countermeasure, reduces the likelihood or impact of harm.

• Residual risk is the risk that remains after controls are applied.

A threat model is a structured account of how a specific system could be harmed. Building one means breaking the system into its parts, identifying its trust boundaries, and asking what could go wrong within each part and at each boundary. The model records what must be protected, who or what could cause harm, which controls reduce the risk, and the assumptions behind those decisions.

Responses to an identified risk fall into four categories:

• Mitigate a risk by reducing its likelihood or impact, although mitigation still leaves residual risk.

• Avoid a risk by stopping the activity that creates it, which may also eliminate a useful service.

• Transfer part of a risk through insurance, contracts, or outsourcing. Transfer may shift financial loss without shifting operational damage, legal responsibility, or reputational harm.

• Accept a risk when it falls within the organization’s tolerance or when further reduction would cost more than the expected harm.

Vulnerabilities, Exploits, and Attacks

These terms describe different stages of a security problem:

• A bug is a defect in hardware or software. Some bugs create vulnerabilities, but vulnerabilities may also result from design choices, configuration, or human behavior.

• A vulnerability is a weakness that could lead to a security failure.

• An exploit is code, a tool, or a technique that takes advantage of a vulnerability.

• An attack is a deliberate attempt to compromise a system.

• A security incident is an event that actually or potentially jeopardizes a security property or violates a policy.

• A data breach is an incident involving unauthorized access to or disclosure of data.

An incident does not have to be a data breach. An availability failure can be a serious security incident even when no information is disclosed.

Spectre, Meltdown, and Rowhammer demonstrate that vulnerabilities can also exist in hardware, where performance features and physical behavior may undermine protections that software relies on.

Exfiltration is the unauthorized transfer of data from a system to a location controlled by an attacker. It is an attack action that compromises confidentiality.

Kinds of Attack

The terms below mix objectives and methods, and most incidents involve several at once:

• Ransomware encrypts data or otherwise disables access to it and demands payment for restoration.

• Extortion uses a threat, such as publishing stolen data, to demand payment or another concession.

• Double extortion combines encryption with a threat to publish stolen data. Backups can restore encrypted files, but they cannot undo the public release of information.

• Denial of service makes a system unusable by exhausting a finite resource or triggering a crash.

• Resource hijacking runs the attacker’s software on someone else’s computer, making the machine itself the target rather than its data.

• Impersonation uses stolen or forged credentials to act as another party. Credential stuffing is one form, replaying username and password pairs from an earlier breach against unrelated sites.

• Social engineering targets a person rather than software.

Attack Surface

An attack surface is the complete set of places where an attacker might attempt to enter a system or produce an effect. A single vulnerability may be reachable through several attack vectors, so closing one path does not necessarily remove the vulnerability.

Hardening reduces the attack surface by removing unused software, disabling unnecessary services, closing ports, and changing insecure defaults. A loosening guide describes the consequences of enabling features that a secure default configuration leaves disabled. Forgotten accounts, applications, services, and permissions remain part of the attack surface even when no one remembers creating them.

An air gap removes direct network connectivity and requires a controlled process to cross the boundary. A Sensitive Compartmented Information Facility (SCIF) controls physical access, electronic devices, sound leakage, and procedures. Some SCIFs also include shielding against radio emissions. Neither control eliminates risks from people, removable media, maintenance, or the supply chain.

Human Factors

Social engineering manipulates a person into providing information or access. Bribery, blackmail, recruitment, and honest mistakes show why human factors cannot be addressed by awareness training alone. Controls must also limit what one person can do, record sensitive actions, and provide a reliable recovery path.

Threats and Threat Actors

A threat may arise from an adversary, an accident, an equipment failure, or a natural event. A threat actor, also known as a threat agent, is a person, group, organization, or state that might carry out an adversarial threat.

Four threat classes describe the effect on a system:

• Disclosure exposes information without authorization.

• Deception causes false information to be accepted as true.

• Disruption interrupts or degrades correct operation.

• Usurpation gives an unauthorized party control of a system or resource.

The Internet as a Risk Amplifier

The Internet amplifies risk through several properties:

• Action at a distance removes the need for physical presence.

• Anonymity and obfuscation make an attacker’s location and identity difficult to determine.

• Global reach places attackers, victims, infrastructure, and money in different jurisdictions.

• Automation at scale allows a single attack to be launched against millions of systems.

• Shared code turns one vulnerability into many potential targets.

• Asymmetric force and effort require defenders to protect every reachable path, while an attacker needs only one that works.

• Lack of distinction means malicious activity can resemble legitimate use.

A botnet is a collection of compromised devices controlled as a group. Its command-and-control (C2) infrastructure distributes instructions and receives results.

The first major Internet worm exposed the need for coordination across organizations. In response, the Computer Emergency Response Team (CERT) was established to coordinate incident response, and many organizations later adopted the model.

Adversaries

An adversary is the person, group, organization, or state pursuing an objective through an attack. Four axes provide a useful description:

1. Goals describe the result the adversary seeks.

2. Risk tolerance describes the exposure and cost the adversary will accept.

3. Resources describe the available money, access, time, personnel, and infrastructure.

4. Expertise describes the adversary’s ability to understand systems and develop attacks.

A threat matrix emphasizes expertise and focus. Focus ranges from opportunistic, where an attacker searches broadly for any vulnerable target, to targeted, where an attacker pursues a selected victim and adapts when defenses hold.

Common labels identify how adversaries operate or what motivates them:

• Hackers probe systems out of curiosity, for profit, or professionally. White hats act under authorization, black hats act without authorization for harmful purposes, and gray hats act without authorization but may claim a defensive purpose.

• Criminal groups conduct fraud, ransomware, extortion, and the sale of access or attack services.

• Malicious insiders intentionally abuse legitimate access they already hold.

• Hacktivists attack to advance a political or social message.

• Industrial spies steal trade secrets for competitors or governments.

• Law enforcement and intelligence agencies seek access for investigation, surveillance, or state objectives under the laws governing them.

• Nation-states fund operations in support of military, intelligence, diplomatic, or economic objectives.

• Script kiddies are low-skilled attackers who rely on tools and instructions created by others.

An advanced persistent threat (APT) is a well-resourced adversary or cluster of actors that pursues significant objectives over an extended period and seeks to maintain or regain access.

Operations, Countermeasures, and Attribution

Cyber espionage primarily seeks information. Cyber warfare primarily seeks effects such as disruption, damage, or loss of control, although there is no universally accepted boundary between the two.

GPS jamming overwhelms satellite signals, preventing a receiver from determining a reliable position or time. GPS spoofing transmits false navigation signals that a receiver accepts as genuine.

Government- and provider-led takedowns operate under legal authority to seize or redirect attacker infrastructure. A private hack-back is an offensive action taken by a victim against an apparent attacker. It creates legal and operational risks because the apparent source may be an innocent compromised system.

Attribution is the process of determining who conducted an operation. Reused tools, compromised infrastructure, false flags, and incomplete evidence make attribution uncertain. Analysts therefore compare tactics, techniques, and procedures (TTPs) across incidents rather than relying solely on actor names. Tactics are objectives, techniques are methods, and procedures are specific implementations.

Tracking Vulnerabilities

Defenders need four types of information about a vulnerability: a shared identifier, a measure of technical severity, evidence of exploitation, and a way to determine whether the affected product is in use. No single source provides all four, so vulnerability management combines identifiers, severity scores, exploitation data, and local system information.

Two tracking concepts form the core vocabulary:

• Common Vulnerabilities and Exposures (CVE) provides a shared identifier for a vulnerability.

• Common Vulnerability Scoring System (CVSS) rates a vulnerability’s technical severity under stated assumptions.

CVE identifies which vulnerability is being discussed. CVSS describes its technical severity, but it does not measure risk to a particular organization.

Two common sources add information beyond CVE identifiers and CVSS scores:

• The National Vulnerability Database (NVD) adds product, severity, and classification data to CVE records.

• The Known Exploited Vulnerabilities (KEV) catalog records vulnerabilities with reliable evidence of exploitation in the wild. The Cybersecurity and Infrastructure Security Agency (CISA), an agency of the Department of Homeland Security, maintains the catalog.

Technical severity does not determine organizational risk on its own. Defenders must also consider whether the product is installed, whether it is exposed, what asset it supports, whether exploitation is occurring, and which controls already protect it.

Vulnerability tracking usually follows this sequence, although attackers and defenders do not wait for the steps to happen in order:

1. Discovery occurs when someone finds a vulnerability.

2. Reporting brings the vulnerability to the vendor or another coordinating organization.

3. Investigation confirms the vulnerability and identifies the affected products and versions.

4. Assignment gives the vulnerability a CVE identifier.

5. Publication adds the CVE record to the public catalog.

6. Scoring describes technical severity with CVSS.

7. Enrichment adds product, weakness, and other contextual information.

8. Mitigation supplies and applies a patch or workaround.

9. Exploitation tracking records confirmed exploitation or estimates its likelihood.

A zero-day vulnerability is previously unknown to the vendor or defenders. A zero-day attack exploits that vulnerability before defenders have time to prepare. The absence of a patch does not by itself make a vulnerability a zero-day.

What You Don’t Need to Study

The lecture notes include the following material to establish scale, provide context, or introduce topics covered later:

• Dates, payment amounts, damage estimates, victim counts, and numbers of affected systems establish scale and chronology rather than define concepts.

• Timelines and technical mechanics of incidents in the case-study sidebars illustrate principles discussed in the main text.

• How Spectre, Meltdown, and Rowhammer work. They appear only to show that vulnerabilities can exist in hardware.

• Injection attacks, ransomware, and AI attacks will be covered in more detail later in the course.

• Vendor-specific mappings among APT numbers, weather names, animal names, and newer Google names demonstrate the absence of a standard naming system.

• CVSS score ranges and the operational details of NVD and KEV are background material. Only their purposes and the difference between them belong here.

• EPSS and LEV illustrate how defenders can estimate exploitation beyond confirmed reports.

• Names of specific malware, such as Mirai and Stuxnet, along with the ransomware groups, intelligence contractors, security vendors, and stolen government tools, provide context for the incidents.