# SQL Injection

SQL Injection (SQLi) is a web security vulnerability that allows an attacker to manipulate a website’s database by injecting malicious SQL queries. It occurs when an application improperly handles user input in SQL statements, leading to unauthorized access, data leaks, or even full database control.

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### **Types of SQL Injection**

1. **In-Band SQLi (Classic)**
   * **Error-Based**: Extracts data via database errors.
   * **Union-Based**: Uses `UNION` to merge results from different tables.
2. **Inferential SQLi (Blind)**
   * **Boolean-Based**: Alters queries to return different responses.
   * **Time-Based**: Uses delays to infer data.
3. **Out-of-Band SQLi**
   * Uses external channels (DNS, HTTP) to exfiltrate data.

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## Common Injection Points

* **Web Forms**
  * Login, Signup, Search, Email Fields, Contact Forms
* **Cookies, Session Data**
  * If cookies store SQL queries or user IDs without sanitization, they can be modified to trigger SQL injection.
* **URL Query Parameters**
* **HTTP Headers**
  * Some applications log user agent strings, referers, or other headers into a database.
* **Log Files & Debugging Interfaces**
  * If logs are stored in the database and an attacker injects
* **File Upload Fields**
  * If file metadata (e.g., filename, EXIF data) is inserted into a database.

**Where SQLi Occurs in Queries:**

* `WHERE` clause in `SELECT` statements (most common).
* `UPDATE` statements (`SET` values or `WHERE` clause).
* `INSERT` statements (values being inserted).
* `ORDER BY` clause (used in sorting).

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## **Impact of SQL Injection**

* **Data theft**: User credentials, credit card details, sensitive info.
* **Authentication bypass**: Logging in without valid credentials.
* **Database takeover**: Extract, modify, or delete entire tables.
* **Persistent backdoors**: Long-term system compromise.
* **Regulatory fines & reputational damage**: GDPR violations, loss of user trust.

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