SQL Injection:iBatis Data Map

ABSTRACT

Constructing a dynamic SQL statement with user input could allow an attacker to modify the statement's meaning or to execute arbitrary SQL commands.

EXPLANATION

SQL injection errors occur when:

1. Data enters a program from an untrusted source.

2. The data is used to dynamically construct a SQL query.



iBatis Data Maps allow you to specify dynamic parameters in SQL statements and are typically defined by using the # characters, like this:

    <select id="getItems" parameterClass="MyClass" resultClass="items">


        SELECT * FROM items WHERE owner = #userName#


    </select>

The # characters around the variable name indicate that iBatis will create a parameterized query with the userName variable. However, iBatis also allows you to concatentate variables directly to SQL statements using $ characters, opening the door for SQL injection.

Example 1: The following code dynamically constructs and executes a SQL query that searches for items matching a specified name. The query restricts the items displayed to those where the owner matches the user name of the currently-authenticated user.

    <select id="getItems" parameterClass="MyClass" resultClass="items">


        SELECT * FROM items WHERE owner = #userName# AND itemname = '$itemName$'


    </select>

However, because the query is constructed dynamically by concatenating a constant base query string and a user input string, the query only behaves correctly if itemName does not contain a single-quote character. If an attacker with the user name wiley enters the string "name' OR 'a'='a" for itemName, then the query becomes the following:

	SELECT * FROM items


	WHERE owner = 'wiley'


	AND itemname = 'name' OR 'a'='a';

The addition of the OR 'a'='a' condition causes the where clause to always evaluate to true, so the query becomes logically equivalent to the much simpler query:

	SELECT * FROM items;

This simplification of the query allows the attacker to bypass the requirement that the query only return items owned by the authenticated user; the query now returns all entries stored in the items table, regardless of their specified owner.

Example 2: This example examines the effects of a different malicious value passed to the query constructed and executed in Example 1. If an attacker with the user name wiley enters the string "name'; DELETE FROM items; --" for itemName, then the query becomes the following two queries:

	SELECT * FROM items


	WHERE owner = 'wiley'


	AND itemname = 'name';




	DELETE FROM items;




	--'

Many database servers, including Microsoft(R) SQL Server 2000, allow multiple SQL statements separated by semicolons to be executed at once. While this attack string results in an error on Oracle and other database servers that do not allow the batch-execution of statements separated by semicolons, on databases that do allow batch execution, this type of attack allows the attacker to execute arbitrary commands against the database.

Notice the trailing pair of hyphens (--), which specifies to most database servers that the remainder of the statement is to be treated as a comment and not executed [4]. In this case the comment character serves to remove the trailing single-quote left over from the modified query. On a database where comments are not allowed to be used in this way, the general attack could still be made effective using a trick similar to the one shown in Example 1. If an attacker enters the string "name'); DELETE FROM items; SELECT * FROM items WHERE 'a'='a", the following three valid statements will be created:

	SELECT * FROM items


	WHERE owner = 'wiley'


	AND itemname = 'name';




	DELETE FROM items;




	SELECT * FROM items WHERE 'a'='a';

One traditional approach to preventing SQL injection attacks is to handle them as an input validation problem and either accept only characters from a whitelist of safe values or identify and escape a blacklist of potentially malicious values. Whitelisting can be a very effective means of enforcing strict input validation rules, but parameterized SQL statements require less maintenance and can offer more guarantees with respect to security. As is almost always the case, blacklisting is riddled with loopholes that make it ineffective at preventing SQL injection attacks. For example, attackers can:

- Target fields that are not quoted

- Find ways to bypass the need for certain escaped meta-characters

- Use stored procedures to hide the injected meta-characters

Manually escaping characters in input to SQL queries can help, but it will not make your application secure from SQL injection attacks.

Another solution commonly proposed for dealing with SQL injection attacks is to use stored procedures. Although stored procedures prevent some types of SQL injection attacks, they fail to protect against many others. Stored procedures typically help prevent SQL injection attacks by limiting the types of statements that can be passed to their parameters. However, there are many ways around the limitations and many interesting statements that can still be passed to stored procedures. Again, stored procedures can prevent some exploits, but they will not make your application secure against SQL injection attacks.

< 출처: http://www.fortify.com/vulncat/en/vulncat/java/sql_injection_ibatis_data_map.html >

현재 참여하고 있는 프로젝트에서 IBATIS 프레임워크를 사용하고 있습니다.

우연히 IBATIS SQL Injection에 대한 자료가 있길래 흥미롭게 읽다가 이렇게 블로그에 옮겨 봅니다.

참고로 영문 자료로 되어있지만 어렵지 않게 이해할수 있기때문에 기타 설명은 달지 않겠습니다.

짧은 영어실력이고 ㅡㅡ; 정리해서 올릴 시간적 여건이 안되기에..(핑계입니다. ㅠㅠ)

담에 시간날때 다시 보고 정리해야 겠습니다.