CS 50 Introduction to Cybersecurity: Software Security

Introduction & Phishing

• Lecturer: David Malan
• Topic: Securing software (software you use and write)
• Example: Phishing (attacking and noticing attacks)
• HTML Basics:
  • Hypertext Markup Language, simple example, tags (open tag/start tag <p>, closing tag/end tag </p>)
  • Tags used: <p>, <script>, <a>
• Threats:
  • Creating malicious links misrepresenting actual links
  • Checking URLs by hovering (not clicking immediately)
  • Example of spoof sites (Yale vs. fake Harvard)

Cross Site Scripting (XSS)

• Concept: Tricking websites into executing your scripts (JavaScript) using their inputs
• Examples of XSS:
  • Example of using <script> tags inside user inputs
  • Impact (inserting scripts like alert('attack'))
• Threats and Protections:
  • Reflected attacks (user input is reflected back and executed in another context)
  • Stored attacks (data input store in database and executed when retrieved)
  • Mitigating XSS attacks using character escapes (e.g., < for <)
  • HTTP Headers (Content-Security-Policy) to restrict execution of inline scripts and styles

Code Injection Attacks

• SQL Injection:

  • Example: select * from users where username = 'username' and password = 'password'
  • Example attack input: '; DELETE FROM users; --
  • Effect of a successful SQL injection (deleting data, retrieving wrong data)
  • Defense: Prepared Statements (using placeholders to safely include user input)

• Command Injection:

  • Using functions like system() and eval() can be dangerous
  • Best Practice: Avoiding direct execution of user inputs as system commands

Cross Site Request Forgery (CSRF)

• Concept: Tricking users into performing actions they did not intend
• Examples of GET and POST requests:
  • GET request example: URL contains all necessary information
  • POST request example: using forms (<form> with method="post")
• Defense:
  • Using CSRF tokens to validate authenticity of requests
  • Avoiding GET for state-changing operations

Secure Software Practices

• Open Source vs. Closed Source:
  • Open Source: Readable by all, potential for better scrutiny but also for attacks
  • Closed Source: Internal only, harder to attack but less community verification
• Trusted Sources:
  • Using App Stores (i.e., Apple App Store, Google Play Store)
  • Ensuring downloaded apps are from legitimate sources
• Digital Signatures:
  • Verifying software with digital signatures (using cryptographic techniques)

Package Managers & Bug Bounties

• Package Managers:
  • Examples: pip (Python), gem (Ruby), npm (Node.js)
  • Ensuring packages are signed and verified
• Bug Bounties:
  • Encouragement of ethical hacking to discover and report bugs for rewards

Final Considerations

• Keeping Track of Vulnerabilities:
  • Common Vulnerabilities and Exposures (CVE)
  • Common Vulnerability Scoring System (CVSS)
  • Exploit Prediction Scoring System (EPSS)
  • Known Exploited Vulnerability Catalog (KEV)