JavaScript Interview Questions
  • JavaScript Interview Questions
  • Contact
  • Introduction
  • Question 1
  • Question 2
  • Question 3
  • Question 4
  • Question 5
  • Question 6
  • Question 7
  • Question 8
  • Question 9
  • Question 10
  • Question 11
  • Question 12
  • Question 13
  • Question 14
  • Question 15
  • Question 16
  • Question 17
  • Question 18
  • Question 19
  • Question 20
  • Question 21
  • Question 22
  • Question 23
  • Question 24
  • Question 25
  • Question 26
  • Question 27
  • Question 28
  • Question 29
  • Question 30
  • Question 31
  • Question 32
  • Question 33
  • Question 34
  • Question 35
  • Question 36
  • Question 37
  • Question 38
  • Question 39
  • Question 40
  • Question 41
  • Question 42
  • Question 43
  • Question 44
  • Question 45
  • Question 46
  • Question 47
  • Question 48
  • Question 49
  • Question 50
  • Question 51
  • Question 52
  • Question 53
  • Question 54
  • Question 55
  • Question 56
  • Question 57
  • Question 58
  • Question 59
  • Question 60
  • Question 61
  • Question 62
  • Question 63
  • Question 64
  • Question 65
  • Question 66
  • Question 67
  • Question 68
  • Question 69
  • Question 70
  • Question 71
  • Question 72
  • Question 73
  • Question 74
  • Question 75
  • Question 76
  • Question 77
  • Question 78
  • Question 79
  • Question 80
  • Question 81
  • Question 82
  • Question 83
  • Question 84
  • Question 85
  • Question 86
  • Question 87
  • Question 88
  • Question 89
  • Question 90
  • Question 91
  • Question 92
  • Question 93
  • Question 94
  • Question 95
  • Question 96
  • Question 97
  • Question 98
  • Question 99
  • Question 100
  • Epilogue
Powered by GitBook
On this page
  • Question
  • Answer

Question 86

Question

What are the security implications of using eval() and new Function()?

Answer

Security Implications:

Both eval() and new Function() allow you to execute arbitrary code dynamically. This flexibility comes with a significant security risk if you don't handle it carefully:

  • Code Injection: The most serious danger is the possibility of code injection attacks. If an attacker can control the string passed to eval() or new Function(), they could inject malicious code into your application. This code could steal sensitive data, modify website content, take control of user accounts, or perform other harmful actions.

  • Unpredictable Behavior: Evaluating untrusted code can lead to unexpected behavior and vulnerabilities. Code might try to access private variables, modify system settings, or trigger unintended side effects that compromise your application's integrity.

Illustrative Example (Vulnerability):

Imagine a website with a feature where users can submit custom JavaScript snippets for display:

const userCode = document.getElementById("userInput").value;
eval(userCode); // Extremely dangerous!

If an attacker enters malicious code like document.cookie = "username=hacker";, it would be executed, potentially stealing the user's cookie data.

Mitigating Risks:

  • Avoid Use Whenever Possible: The best practice is to avoid eval() and new Function() altogether. Find alternative, safer ways to achieve your goal.

  • Sanitize Input: If you absolutely must use them, rigorously sanitize any user-provided input before passing it to these functions. This involves removing potentially harmful characters or code snippets. Libraries like DOMPurify can help with this process.

  • Isolate Execution: Consider running untrusted code in a sandboxed environment (e.g., using Web Workers) to limit its access to sensitive data and system resources.

Recommendations:

  • Prioritize writing your code without relying on dynamic code execution. Use built-in JavaScript features and libraries whenever possible.

  • If you encounter eval() or new Function() in existing code, carefully assess the context and consider refactoring it for security.

PreviousQuestion 85NextQuestion 87

Last updated 9 months ago