Improper Neutralization of Special Elements in Data Query Logic

Description

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

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.

...
string userName = ctx.getAuthenticatedUserName();
string query = "SELECT * FROM items WHERE owner = '" + userName + "' AND itemname = '" + ItemName.Text + "'";
sda = new SqlDataAdapter(query, conn);
DataTable dt = new DataTable();
sda.Fill(dt);
...

The query that this code intends to execute follows:

SELECT * FROM items WHERE owner = <userName> AND itemname = <itemName>;

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 Two

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

context = new InitialDirContext(env);
String searchFilter = "StreetAddress=" + address;
NamingEnumeration answer = context.search(searchBase, searchFilter, searchCtls);

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 Three

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

<users>
  <user>
    <login>john</login>
    <password>abracadabra</password>
    <home_dir>/home/john</home_dir>
  </user>
  <user>
    <login>cbc</login>
    <password>1mgr8</password>
    <home_dir>/home/cbc</home_dir>
  </user>
</users>

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

XPath xpath = XPathFactory.newInstance().newXPath();
XPathExpression xlogin = xpath.compile("//users/user[login/text()='" + login.getUserName() + "' and password/text() = '" + login.getPassword() + "']/home_dir/text()");
Document d = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(new File("db.xml"));
String homedir = xlogin.evaluate(d);

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

//users/user[login/text()='john' or ''='' and password/text() = '' or ''='']/home_dir/text()

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

See Also