6.5 Security threats and countermeasures

Operating systems face numerous security threats, from malware to social engineering attacks. These risks can compromise system integrity, steal data, or disrupt operations. Understanding these threats is crucial for implementing effective countermeasures and protecting valuable resources.

Security design principles and mechanisms form the foundation of robust OS protection. By applying concepts like least privilege, defense-in-depth, and encryption, systems can better withstand attacks. Implementing these measures requires careful consideration of usability, scalability, and compliance requirements.

Operating System Security Threats

Malware and Social Engineering Attacks

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• Malware compromises system integrity, steals data, or disrupts operations
  • Viruses replicate and spread by attaching to other files or programs
  • Worms self-replicate and spread across networks without user interaction
  • Trojans disguise as legitimate software to trick users into installation
  • Ransomware encrypts user data and demands payment for decryption (WannaCry)
• Social engineering exploits human vulnerabilities to gain unauthorized access
  • Phishing uses fake emails or websites to steal credentials (fake bank login pages)
  • Pretexting creates false scenarios to manipulate targets into divulging information
  • Baiting offers something enticing to lure victims into a trap (malware-infected USB drives)

Technical Exploits and Network Attacks

• Buffer overflow attacks exploit memory vulnerabilities
  • Overwrite adjacent memory locations with malicious code
  • Can lead to arbitrary code execution or system crashes
  • Often target input fields or network protocols with insufficient bounds checking
• Denial-of-Service (DoS) and Distributed Denial-of-Service (DDoS) overwhelm system resources
  • Flood servers with excessive traffic or requests
  • Render services unavailable to legitimate users
  • DDoS attacks use multiple compromised systems (botnets) for increased impact
• Privilege escalation allows attackers to gain higher-level permissions
  • Vertical escalation increases access rights (user to admin)
  • Horizontal escalation accesses resources of another user at the same level
  • Can lead to full system compromise if successful
• Man-in-the-middle attacks intercept and potentially alter communications
  • Compromise data confidentiality and integrity
  • Often exploit unsecured Wi-Fi networks or DNS spoofing
  • Can be used for eavesdropping or injecting malicious content
• Zero-day exploits target previously unknown vulnerabilities
  • Pose significant risks due to lack of available patches or defenses
  • Often sold on black markets or used in advanced persistent threats (APTs)
  • Require rapid response and patching from software vendors

Secure System Design Principles

Core Security Design Concepts

• Principle of least privilege limits user and process permissions
  • Reduces potential impact of security breaches
  • Restricts access to only necessary resources for each user or process
  • Implements concepts like role-based access control (RBAC)
• Defense-in-depth implements multiple layers of security controls
  • Protects against various attack vectors
  • Provides redundancy in case of individual control failures
  • Combines firewalls, antivirus, encryption, and other measures
• Separation of duties divides critical functions among different users or processes
  • Prevents single points of failure
  • Reduces risk of insider threats
  • Requires multiple parties to complete sensitive operations (two-person control)

Additional Security Design Principles

• Complete mediation ensures every access to system resources is checked
  • Maintains consistent security enforcement
  • Verifies authorization for each resource request
  • Implements access control lists (ACLs) or capability-based security
• Fail-safe defaults configure systems to deny access by default
  • Requires explicit permissions for resource access
  • Reduces risk of accidental exposures
  • Aligns with the principle of least privilege
• Economy of mechanism keeps security designs and implementations simple
  • Minimizes potential vulnerabilities
  • Eases security analysis and auditing
  • Reduces complexity-induced errors in implementation
• Open design principles advocate for security through transparency
  • Allows for peer review and continuous improvement
  • Contrasts with security through obscurity
  • Enables community-driven security enhancements (open-source security tools)

Implementing Security Mechanisms

Authentication and Encryption

• Multi-factor authentication combines two or more independent credentials
  • Significantly enhances access control security
  • Combines something you know (password), have (token), or are (biometrics)
  • Reduces risk of compromised accounts even if one factor is breached
• Public Key Infrastructure (PKI) provides a framework for secure communication
  • Uses digital certificates and public-private key pairs
  • Enables encryption and digital signatures
  • Supports secure email (S/MIME) and website connections (HTTPS)
• Access Control Lists (ACLs) define permissions for users and processes
  • Control access to system resources
  • Enforce principle of least privilege
  • Can be implemented at file system, network, or application levels

Network Security and Monitoring

• Intrusion Detection Systems (IDS) monitor network or system activities
  • Detect malicious actions or policy violations
  • Alert administrators to potential security breaches
  • Can be network-based (NIDS) or host-based (HIDS)
• Virtual Private Networks (VPNs) create secure, encrypted tunnels
  • Ensure data confidentiality over untrusted networks
  • Enable secure remote access to protected networks
  • Use protocols like IPsec or SSL/TLS for encryption
• Firewalls filter network traffic based on predetermined security rules
  • Act as a barrier between trusted internal and potentially hostile external networks
  • Can be hardware appliances, software applications, or cloud-based services
  • Implement stateful inspection, application-layer filtering, or next-generation features
• Security Information and Event Management (SIEM) systems aggregate and analyze log data
  • Detect and respond to security incidents in real-time
  • Correlate events from various sources for comprehensive threat analysis
  • Provide dashboards and reports for security operations teams

Evaluating Security Countermeasures

Assessment and Analysis Techniques

• Penetration testing assesses system security by simulating real-world attacks
  • Identifies vulnerabilities and evaluates existing security measures
  • Can be black box (no prior knowledge) or white box (full system information)
  • Provides actionable insights for improving security posture
• Security metrics and key performance indicators (KPIs) provide quantitative measures
  • Enable data-driven decision-making and continuous improvement
  • Track metrics like mean time to detect (MTTD) or patch compliance rates
  • Help justify security investments to management
• Cost-benefit analysis weighs financial implications of security measures
  • Compares implementation costs against potential breach costs
  • Informs resource allocation decisions
  • Considers factors like regulatory fines and reputational damage

Practical Considerations and Compliance

• Usability considerations in security design balance protection with user experience
  • Overly complex measures may lead to user circumvention
  • Aims to minimize friction in security processes (single sign-on systems)
  • Incorporates user feedback in security policy development
• Scalability of security solutions ensures effectiveness as systems grow
  • Avoids performance bottlenecks or management complexities
  • Considers cloud-based or distributed security architectures
  • Implements automation for security tasks (automated patch management)
• Compliance requirements and industry standards influence security countermeasures
  • Impact effectiveness and associated costs of security measures
  • Include regulations like GDPR, HIPAA, or PCI DSS
  • May require specific security controls or regular audits
• Threat modeling techniques assess potential vulnerabilities and attack vectors
  • Guide prioritization and selection of security countermeasures
  • Use methodologies like STRIDE or PASTA for systematic analysis
  • Help focus resources on most critical risks based on likelihood and impact