What is SQL Injection?

SQL injection (SQLi) is an attack where someone exploits a web app’s input fields to run unauthorized SQL queries on its database. It happens when user input isn’t properly cleaned up before being added to a SQL statement, letting attackers manipulate the query’s logic. They might aim to steal data (like usernames or passwords), change records, or bypass login screens.

Here’s a basic example:

• A login form’s backend query might look like this:

SELECT * FROM users WHERE username = 'user' AND password = 'pass';

• If the app doesn’t check input, an attacker could enter this in the password field:

' OR '1'='1

• The query then becomes:

SELECT * FROM users WHERE username = 'user' AND password = '' OR '1'='1';

• Since ‘1’=’1′ is always true, the attacker logs in without a real password.

Attackers can push it further:

• To dump data: ‘ UNION SELECT * FROM sensitive_table —
• To delete stuff: ‘; DROP TABLE users; —

How Does It Work on the Client Side?

From the client side—think of an attacker using a browser or a tool—SQL injection is about sending tricky input through the app’s front-end (like forms or URLs) to mess with the server’s database. Here’s the breakdown:

1. Finding Weak Spots:
   • The attacker scans the website for input areas: login fields, search bars, or even URL parameters like example.com/profile?id=123. These are spots where data gets sent to the server and might end up in a SQL query.
2. Building the Attack:
   • They enter something sneaky. For a login password field, maybe: ‘ OR ‘1’=’1. For a URL, maybe: example.com/profile?id=1′ OR ‘1’=’1. The idea is to change how the SQL query runs, guessing at the backend structure.
3. Sending It Off:
   • This input goes to the server via an HTTP request. Examples:
     • A POST request from a form:

POST /login HTTP/1.1
Host: example.com
Content-Type: application/x-www-form-urlencoded

username=admin&password=' OR '1'='1

 - A GET request in a URL:

example.com/search?query=apple' UNION SELECT username,password FROM users --

• Special characters like ‘ might get URL-encoded (e.g., %27), but the effect is the same.

4. Checking the Result:
   • The attacker looks at what comes back. If ‘ OR ‘1’=’1 logs them in, jackpot. If a search bar spits out odd data or an error like “SQL syntax error,” they know the input hit the database raw.
5. Digging Deeper:
   • Using browser dev tools (F12) or something like Burp Suite, they tweak the input. Maybe ‘; DROP TABLE users; –—if the site breaks, they’ve done damage. Automated tools like SQLMap can speed this up, pulling data straight to their screen.

Client-Side Example:
You type test into a site’s search bar—normal results. Then you try test’ OR ‘1’=’1 and get an error like “syntax error near ‘1’”. That’s a clue the app’s vulnerable. Next, you might try test’ UNION SELECT username,password FROM users — and see user data pop up in the results—all from your browser.

Real-World Cases of SQL Injection Attacks

1. Sony Pictures (2011)
   • Hackers used SQLi to leak over 1 million accounts (emails, passwords, etc.) from Sony’s servers via a flawed web app. Huge reputational hit and legal costs followed.
   • Lesson: Big names aren’t immune to simple mistakes.
2. Heartland Payment Systems (2008)
   • SQLi on a payment app exposed 130 million credit card numbers over months, costing over $140 million. Attackers slipped in via unfiltered input.
   • Lesson: Undetected SQLi can bleed data for ages.
3. TalkTalk (2015)
   • A teen exploited SQLi on TalkTalk’s site, leaking 157,000 customers’ data (including bank info). Fined £400,000, it showed how easy SQLi can be.
   • Lesson: Basic attacks still work if defenses are weak.

How to Defend Against SQL Injection

Here’s how to lock it down:

1. Prepared Statements/Parameterized Queries
   • Best defense. Use placeholders instead of raw input. Python example:

query = "SELECT * FROM users WHERE username = ? AND password = ?"
cursor.execute(query, (username, password))

• Keeps input as data, not code. Works in Java (PreparedStatement), PHP (PDO), etc.

2. Input Validation
   • Check input fits expected patterns. Python regex example:

import re
if not re.match("^[a-zA-Z0-9]+$", username):
    raise ValueError("Invalid username")

• Enough? Nope. It catches obvious garbage, but sneaky input like ‘ OR ‘1’=’1 can slip through.

3. Escaping Inputs
   • If stuck without prepared statements, escape characters (e.g., ‘ to \’). Use stuff like mysql_real_escape_string(), but it’s riskier than parameterization.
4. ORMs
   • Tools like SQLAlchemy or Hibernate handle queries safely—if set up right.
5. Least Privilege
   • Limit database rights. Example:

GRANT SELECT ON users TO 'app_user'@'localhost';

• Won’t stop SQLi but caps the damage.

6. Web Application Firewall (WAF)
   • Blocks fishy patterns like UNION SELECT. Good backup, not perfect—attackers can dodge it.
7. Security Audits
   • Test with tools like SQLMap to find holes before attackers do.

Is Input Validation Enough?

Not really. It’s a start—stops some junk input—but doesn’t fix the core problem of input running as code. If you allow letters and numbers, ‘ UNION SELECT still fits. Prepared statements are the real deal; validation’s just extra armor.

Final Thoughts

SQLi is a client-side guessing game that exploits server-side sloppiness. Attackers poke at forms and URLs; you stop them with prepared statements and smart design. For WordPress, if you’re pasting this, use the “Code” block or “Text” mode in the classic editor to keep formatting intact.