Types of XSS Attacks
- Stored XSS Attacks: The attacker permanently stores malicious scripts on the target server. Whenever the user accesses the stored information, the script runs. For example, in a comment section of a blog post, an attacker might post a comment that includes a script.
- Reflected XSS Attacks: The attacker tricks the victim into clicking a link that contains the malicious script. The server includes the script from the URL in the response and sends it to the user's browser to execute.
Preventing XSS Attacks
The best way to prevent XSS attacks is to sanitize all user inputs and outputs. Below are a few steps you can take:
Escaping User Input: This involves making potentially harmful input safe. For example, in PHP, you can use the
$user_input = "<script>alert('XSS')</script>"; echo htmlspecialchars($user_input, ENT_QUOTES, 'UTF-8');
Validating User Input: This means ensuring the user's input meets specific criteria. For example, if you're expecting a date, you should reject all input that doesn't match a date format.
Using HTTP Headers to Restrict Script Execution: The 'Content-Security-Policy' header can be set to disallow inline scripts.
header("Content-Security-Policy: script-src 'self'");
Cross-site scripting attacks are a serious threat that can lead to stolen user data, damaged user trust, and potential legal issues. However, understanding how XSS attacks work and applying correct prevention techniques will help secure your web applications against these types of attacks.
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