Common Weakness Enumeration

Depending on the capabilities of the query language, an attacker could inject additional logic into the query to:

• Modify the intended selection criteria, thus changing which data entities (e.g., records) are returned, modified, or otherwise manipulated
• Append additional commands to the query
• Return more entities than intended
• Return fewer entities than intended
• Cause entities to be sorted in an unexpected way

The ability to execute additional commands or change which entities are returned has obvious risks. But when the product logic depends on the order or number of entities, this can also lead to vulnerabilities. For example, if the query expects to return only one entity that specifies an administrative user, but an attacker can change which entities are returned, this could cause the logic to return information for a regular user and incorrectly assume that the user has administrative privileges.

While this weakness is most commonly associated with SQL injection, there are many other query languages that are also subject to injection attacks, including HTSQL, LDAP, DQL, XQuery, Xpath, and "NoSQL" languages.

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 owner matches the user name of the currently-authenticated user.

The query that this code intends to execute follows:

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:

for itemName, then the query becomes the following:

The addition of the:

condition causes the WHERE clause to always evaluate to true, so the query becomes logically equivalent to the much simpler query:

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

The code below constructs an LDAP query using user input address data:

Because the code fails to neutralize the address string used to construct the query, an attacker can supply an address that includes additional LDAP queries.

Example 3

Consider the following simple XML document that stores authentication information and a snippet of Java code that uses XPath query to retrieve authentication information:

The Java code used to retrieve the home directory based on the provided credentials is:

Assume that user "john" wishes to leverage XPath Injection and login without a valid password. By providing a username "john" and password "' or ''='" the XPath expression now becomes

This lets user "john" login without a valid password, thus bypassing authentication.