Robust and secure programming

Question 1

Steps to install bandit and analyse a piece of code

Answer 1

pip install bandit and bandit -r path/to/your/code

Question 2

Three examples of security flaws that bandit can find

Answer 2

Use of dangerous functions, weak cryptographic practices and insecure deserialization.

Question 3

Name THREE specific techniques that can be used to make programs more robust.

Answer 3

Input validation, error handling and exception management, and defensive programming.

Question 4

Using a code fragment, explain how “Input validation” works

Answer 4

Input validation is the process of ensuring that user inputs meet certain criteria before proceeding with further processing. def get_positive_integer(): try: user_input = int(input(“Enter a positive integer: “)) if user_input <= 0: print(“Error: Please enter a positive integer.”) else: return user_input except ValueError: print(“Error: Input must be an integer.”)

Question 5

Using a code fragment, explain how “Defensive programming” works

Answer 5

Defensive programming is a coding style that anticipates potential errors and incorporates safeguards to prevent them.def calculate_average(numbers): if not isinstance(numbers, list): raise TypeError(“Input must be a list of numbers”) if len(numbers) == 0: return 0 total = 0 for num in numbers: if not isinstance(num, (int, float)): raise TypeError(“All elements in the list must be numbers”) total += num return total / len(numbers)

Question 6

Using a code fragment, explain how “Error handling and exception management” works

Answer 6

Use try/except.def divide_numbers(a, b): try: result = a / b print(“Result of division:”, result) except ZeroDivisionError: print(“Error: Division by zero is not allowed.”) except TypeError: print(“Error: Please provide numeric values for division.”) except Exception as e: print(“An unexpected error occurred:”, e)

Question 7

The following function, written in Python, takes a file name as input and then shows the contents of the file on the screen. Explain why it is not a robust program? Propose TWO different mechanism to make it robust.

Answer 7

It lacks error handling and resource management. Use try and except to catch any errors while opening and using the file. Use a with statement (context manager) to open the file. This ensures that the file handle is automatically closed when the block of code exits, even if an exception occurs. It helps prevent resource leaks and ensures proper cleanup.

Question 8

You have been asked to develop a strategy to evaluate the security of the codebase for the control panel software. Describe THREE actions you would take in carrying out this evaluation.

Answer 8

Code Review and Static Analysis
Penetration Testing and Vulnerability Assessment
Threat Modeling and Risk Analysis.

Question 9

Describe TWO things you should do before including an open-source library in yoursoftware.

Answer 9

Review the License and Assess the Quality and Maintenance.

Question 10

Describe ONE positive and ONE negative of using open source code inyour project.

Answer 10

Positive: Faster Development
Negative: Dependency Risks.

Question 11

Robust Programming in Python

Answer 11

Python has built-in exception handling, optional type hints, and extensive testing ecosystem.

Question 12

Robust Programming in Javascript

Answer 12

Javascript with its evolving error handling capabilities, type safety improvements with TypeScript, and a good collection of testing frameworks.

Question 13

Assume there is a module named UploadFile(path) which takes a string as its parameter (it is the path of a file on your local computer) and then uploads the file to the server. This function has various outcomes depending on if the upload was successful. Write the code that you would use to run the synchronous UploadFile(path)in a way that doesn’t crash if the upload fails (for example if the file does not exist in the given path)

Answer 13

Wrap it in a try/except clause

Question 14

Assume that you are using this piece of code (UploadFile(path)) in a critical system. Thus, you have been asked to conduct a static security audit on the code. Give TWO examples and descriptions of the kind of problems you would expect a static security audit to find.

Answer 14

Input Validation Issues: One common problem that a static security audit may find is inadequate input validation. This includes failing to properly validate user input or external data before processing it. For example, if the UploadFile(path) function does not perform sufficient validation on the input file path, an attacker could potentially manipulate the path to access unauthorised files on the system or exploit path traversal vulnerabilities.

Insecure File Handling: Another issue that a static security audit may uncover is insecure file handling practices. This includes improper file permissions, insecure temporary file creation, or lack of proper file sanitization. For instance, if the UploadFile(path) function does not enforce proper file permissions or sanitization when handling uploaded files, it could allow an attacker to overwrite or execute arbitrary files on the system, leading to unauthorized access or code execution vulnerabilities.

Question 15

Static security audit

Answer 15

The assessment is performed without executing the application’s code. It involves analysing the application’s source code, configuration files, and documentation to identify potential security vulnerabilities, design flaws, or coding errors. Static analysis tools and manual code review techniques are commonly used as well.

Question 16

Dynamic security audit

Answer 16

In a dynamic security audit, the assessment involves actively interacting with the running application to evaluate its security controls and behaviors in real-time. Dynamic analysis tools, penetration testing, and vulnerability scanning are used to simulate attacks, probe for weaknesses, and identify security vulnerabilities that may be exploitable during runtime.

Question 17

Give TWO examples and descriptions of the kind of problems you would expect a static security audit to find.

Answer 17

Injection vulnerabilities, such as SQL injection.

Sensitive information, such as passwords or API keys is mishandled or exposed in the application’s source code.

Question 18

Secure Programming with Python

Answer 18

Python’s built-in features and libraries for secure coding practices, such as input validation, secure random number generation, and cryptographic functions. Strong typing and dynamic runtime checks help prevent common security vulnerabilities, such as type confusion and buffer overflows.

Question 19

Secure Programming with Javascript

Answer 19

Best practices such as using strict mode, input validation, and sanitisation, help mitigate security risks.

Question 20

You have used the bandit code analyser to detect problems in Python code. Present a code fragment in python which illustrates a problem that bandit can detect.

Answer 20

def delete_file(filename): os.system(“rm “ + filename)

Question 21

You are writing code for a webserver in JavaScript that should keep running at all costs. There is a risky function that queries a database that is unreliable. Write the code you would use to run the synchronous ‘checkDatabase()’ function in a way that does not crash the program if it fails.

Answer 21

Wrap the function checkDatabase() in a try-catch block. try { checkDatabase(); } catch (error) { console.error(“Error checking database”);}