Segfault ethical hacking week 11-2

 

Understanding XSS (Cross-Site Scripting): A Deep Dive

1. Overview of XSS Mitigation Strategies

Including an overview table at the beginning helps readers quickly grasp the main concepts. For example:

Category	Method	Advantages	Disadvantages
Blacklist Filtering	Block specific strings/patterns	Flexible	Easy to bypass
Whitelist Filtering	Allow only specific strings/tags	Very secure	Highly restricts user input
HTML Entity Encoding	Escape special characters	Prevents script execution	Limits input freedom

2. Concrete HTML Entity Encoding Examples

Adding a reference table makes this more intuitive:

Character	Entity
<	&lt;
>	&gt;
&	&amp;
"	&quot;
'	&#x27;
/	&#x2F;

3. Event Handler Reference

A list of common event handler attributes is especially important for beginners. You can organize them in a table:

Event	Description
onerror	Executes on resource load failure
onload	Executes when loading is complete
onclick	Executes on click
onmouseover	Executes on mouse over
onfocus	Executes when an element gains focus
onblur	Executes when an element loses focus

There are over 50 different event attributes, so in whitelist filtering, you should explicitly allow only those that are strictly necessary.

4. Introducing Content Security Policy (CSP)

Recently, CSP configuration has become a core part of XSS defense. A brief overview is helpful:

• What is CSP?

  • A security policy that instructs the browser which resources are allowed to load.

• Example HTTP Header

  Content-Security-Policy: default-src 'self'; script-src 'self';
  

  • default-src 'self': Only allow resources from your own domain.

  • script-src 'self': Block external scripts.

• Advantages

  • Blocks script injection effectively.

• Disadvantages

  • Can be disruptive when retrofitted to existing services.

Adding this section will improve the professional credibility of your article.

5. HTTP Only / Secure Cookie Flags

It’s also worth mentioning cookie protection settings that are frequently discussed alongside XSS mitigation:

• HttpOnly: Prevents JavaScript from accessing cookies.

• Secure: Sends cookies only over HTTPS.

• SameSite: Restricts cross-site request cookies.

Example:

Set-Cookie: session=...; HttpOnly; Secure; SameSite=Strict

6. Brief Introduction to DOM-based XSS

Most examples you shared are Reflected or Stored XSS. It helps to briefly introduce DOM-based XSS as well:

• What is DOM-based XSS?

  • Occurs when client-side scripts process untrusted input (e.g., location, document.write) without sanitization.

• Example

  var q = location.hash.substr(1);
  document.getElementById("result").innerHTML = q;
  

  → If you navigate to #<img src=x onerror=alert(1)>, the script executes.