Why Is the eval() Function Dangerous?

The reason eval is generally considered dangerous is because it is very easy for untrusted code to sneak in.

Imagine you have a web application that takes user input to perform a calculation using eval(). The application prompts the user to enter a mathematical expression, which is then evaluated using eval():

const userInput = prompt("Enter a mathematical expression:");
const result = eval(userInput);
console.log("Result:", result);

Now, a well-intentioned user might enter a valid mathematical expression, such as 2 + 3, and the application would correctly evaluate and display the result.

However, this usage of eval() becomes risky when an attacker provides malicious input.

Suppose the attacker enters the following string:

alert("Dangerous code executed!");

If the application blindly uses eval() on this input, it will execute the attacker's JavaScript code, resulting in an alert dialog displaying the message "Dangerous code executed!".

This is a simple example, but it illustrates the potential for code injection. In a real-world scenario, an attacker might attempt more harmful actions, such as stealing sensitive information, manipulating data, or executing actions on behalf of the user.

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