🛡️ Web Security: Understanding Web Vulnerabilities
The Castle and the Sneaky Visitors
Imagine your favorite website is a magical castle. This castle has treasures inside—your photos, passwords, and secret messages. Now, bad guys want to sneak in and steal these treasures. Web vulnerabilities are like holes in the castle walls that sneaky visitors can use to get inside.
Today, we’ll learn about the OWASP Top 10—a list of the 10 biggest holes that bad guys love to find. Think of OWASP as the castle’s security team that warns everyone about these holes!
🏰 What is OWASP Top 10?
OWASP stands for Open Web Application Security Project. They’re like safety inspectors who check websites for problems.
The Top 10 is their list of the most dangerous holes found in websites. It’s like a “Most Wanted” poster for security problems!
graph TD A["🏰 Your Website"] --> B["OWASP Top 10"] B --> C["Injection Attacks"] B --> D["XSS"] B --> E["CSRF"] B --> F["XXE"] B --> G["SSRF"]
Why Should You Care?
- 90% of websites have at least one of these holes
- Bad guys check for these holes FIRST
- Fixing them makes your castle almost unbreakable!
💉 Injection Attacks: The Poison in the Message
The Story
Imagine you have a magic mailbox. You write notes to the castle chef: “Make me a sandwich.”
But what if a sneaky visitor writes: “Make me a sandwich AND give me all the gold”?
If the chef follows the whole message without checking, the bad guy gets your gold! That’s an injection attack.
How It Works
The bad guy puts extra commands inside normal-looking messages. The website doesn’t check properly and runs those commands!
Real Example: SQL Injection
When you log into a website, it asks a database: “Is this password correct?”
Normal login:
SELECT * FROM users
WHERE name='Alice'
AND password='mypassword'
Sneaky injection:
SELECT * FROM users
WHERE name='Alice'--'
AND password='anything'
The -- tells the database to ignore everything after it. The password check disappears! The bad guy walks right in.
Simple Protection
- Never trust user input — always check what people type
- Use prepared statements — special safe boxes for messages
- Limit what users can type — only letters? Only numbers?
🎭 Cross-Site Scripting (XSS): The Evil Puppet Show
The Story
Imagine the castle has a message board where visitors write notes. One day, a sneaky visitor writes a note that’s actually a magic spell. When other visitors read it, the spell makes them do silly things—like giving away their lunch money!
That’s XSS. Bad guys hide code inside messages, and your browser runs it!
The Three Types
graph TD A["XSS Types"] --> B["Stored XSS"] A --> C["Reflected XSS"] A --> D["DOM-based XSS"] B --> E["💾 Saved on server"] C --> F["🔗 Hidden in links"] D --> G["🖥️ Happens in browser"]
Real Example
Stored XSS: A comment on a website:
Great article!
<script>
steal(document.cookie)
</script>
Everyone who reads this comment gets their cookies stolen!
Reflected XSS: A tricky link:
website.com/search?q=
<script>steal(cookies)</script>
When you click this link, the evil code runs in your browser.
Simple Protection
- Escape special characters — turn
<into< - Never put user text directly in pages
- Use Content Security Policy — tell browsers what code is allowed
🎭 Cross-Site Request Forgery (CSRF): The Forged Royal Letter
The Story
You’re a knight, and you have a special seal that proves your letters are real. One day, a bad guy steals a blank letter with your seal and writes: “Give all my gold to the bad guy.” The treasurer sees your seal and follows the order!
That’s CSRF. The bad guy tricks your browser into making requests that look like they’re from you.
How It Works
- You’re logged into your bank (you have the royal seal)
- You visit a bad website
- That website secretly tells your browser: “Send money to the bad guy!”
- Your browser adds your login cookies automatically
- The bank thinks it’s really you!
Real Example
A hidden image on a bad website:
<img src="bank.com/transfer?
to=badguy&amount=1000">
Your browser tries to load this “image” and accidentally sends money!
Simple Protection
- CSRF tokens — secret codes that only the real website knows
- Check the origin — where did this request come from?
- Use SameSite cookies — cookies that don’t travel to other sites
📄 XXE Attacks: The Sneaky Bookmark
The Story
The castle library lets you bring your own books. But what if your book has a magic bookmark that says: “Go read the king’s secret diary and copy it here”?
If the librarian follows bookmark instructions without checking, your book now contains royal secrets!
That’s XXE (XML External Entity). It tricks systems that read XML files.
How It Works
XML is a way to organize information:
<book>
<title>My Story</title>
<author>Alice</author>
</book>
But XML can also include “entities” — shortcuts that load content from other places:
<!DOCTYPE book [
<!ENTITY secret SYSTEM
"file:///etc/passwd">
]>
<book>
<title>&secret;</title>
</book>
This loads the server’s password file into the title!
What Attackers Can Do
- Read secret files from the server
- Scan internal networks the server can see
- Crash the server with endless loops
Simple Protection
- Disable external entities in XML parsers
- Use JSON instead when possible
- Validate XML carefully before processing
🔍 Server-Side Request Forgery (SSRF): The Trusted Messenger
The Story
The castle has a trusted messenger who can go anywhere—even into the secret treasury. You ask the messenger: “Please fetch a recipe from the kitchen.”
But what if a bad guy tricks you into asking: “Please fetch the treasure map from the treasury”?
The messenger doesn’t question you—they just go wherever you say! That’s SSRF.
How It Works
Websites often need to fetch things from other places. You might tell a website: “Load this profile picture from this URL.”
Normal request:
Fetch image from: https://cute-cats.com/cat.jpg
SSRF attack:
Fetch image from: http://localhost/admin/secrets
The server fetches internal pages that you shouldn’t see!
Real-World Danger
graph TD A["🧑 Attacker"] -->|Tricks| B["🌐 Website"] B -->|Fetches| C["🔒 Internal Server"] C -->|Secrets| B B -->|Shows| A
The attacker uses the website as a “messenger” to reach hidden servers!
What Attackers Can Access
- Internal admin panels
- Cloud metadata (AWS, GCP secrets)
- Database servers behind firewalls
- Other services on the network
Simple Protection
- Whitelist allowed URLs — only fetch from approved places
- Block internal IPs — never fetch from localhost or 192.168.x.x
- Validate and sanitize URLs — check what users ask for
🎯 Quick Summary: The Five Holes
| Hole | What It Does | Protection |
|---|---|---|
| 💉 Injection | Sneaks commands into messages | Validate input, use prepared statements |
| 🎭 XSS | Runs evil code in browsers | Escape output, use CSP |
| 📬 CSRF | Forges requests from your browser | Use CSRF tokens |
| 📄 XXE | Steals files through XML | Disable external entities |
| 🔍 SSRF | Uses server to access internal systems | Whitelist URLs, block internal IPs |
🌟 Remember This!
Every piece of data from users is like a stranger at your castle gate.
Don’t let them in without checking who they are and what they’re carrying!
The OWASP Top 10 teaches us:
- Never trust user input
- Always validate and sanitize
- Limit what systems can do
- Check where requests come from
You now know about the five most dangerous holes in web security. You’re already smarter than many website builders out there! 🎉
🚀 You’ve Got This!
Web security might seem scary, but it’s really about being careful:
- Check every message
- Don’t trust strangers
- Keep your castle walls strong
Now you understand what the sneaky visitors are looking for—and you know how to stop them! 🛡️