A SQL injection vulnerability arises when the original SQL query can be altered to form an altogether different query. Execution of this altered query may result in information leaks or data modification. The primary means of preventing SQL injection are sanitizing and validating untrusted input and parameterizing queries.
Suppose a database contains user names and passwords used to authenticate users of the system. A SQL command to authenticate a user might take the following form:
SELECT * FROM db_user WHERE username='<USERNAME>' AND
password='<PASSWORD>'
If it returns any records, the user name and password are valid.
However, if an attacker can substitute arbitrary strings for <USERNAME> and <PASSWORD>, they can perform a SQL injection by using the following string for <USERNAME>:
validuser' OR '1'='1
When injected into the command, the command becomes
SELECT * FROM db_user WHERE username='validuser' OR '1'='1' AND password=<PASSWORD>
If validuser is a valid user name, this SELECT statement selects the validuser record in the table. The password is never checked because username='validuser' is true; consequently, the items after the OR are not tested. As long as the components after the OR generate a syntactically correct SQL expression, the attacker is granted the access of validuser.
Likewise, an attacker could supply a string for <PASSWORD> such as
' OR '1'='1
This would yield the following command:
SELECT * FROM db_user WHERE username='' AND password='' OR '1'='1'
This time, the '1'='1' tautology disables both user name and password validation, and the attacker is falsely logged in without a correct login ID or password.
Noncompliant Code Example
This noncompliant code example shows JDBC code to authenticate a user to a system. The password is passed as a char array, the database connection is created, and then the passwords are hashed.
Unfortunately, this code example permits a SQL injection attack by incorporating the unsanitized input argument username into the SQL command, allowing an attacker to inject validuser' OR '1'='1. The password argument cannot be used to attack this program because it is passed to the hashPassword() function which also sanitizes the input.
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
class Login {
public Connection getConnection() throws SQLException {
DriverManager.registerDriver(new
com.microsoft.sqlserver.jdbc.SQLServerDriver());
String dbConnection =
PropertyManager.getProperty("db.connection");
// Can hold some value like
// "jdbc:microsoft:sqlserver://<HOST>:1433,<UID>,<PWD>"
return DriverManager.getConnection(dbConnection);
}
String hashPassword(char[] password) {
// Create hash of password
}
public void doPrivilegedAction(String username, char[] password)
throws SQLException {
Connection connection = getConnection();
if (connection == null) {
// Handle error
}
try {
String pwd = hashPassword(password);
String sqlString = "SELECT * FROM db_user WHERE username = '"
+ username +
"' AND password = '" + pwd + "'";
Statement stmt = connection.createStatement();
ResultSet rs = stmt.executeQuery(sqlString);
if (!rs.next()) {
throw new SecurityException(
"User name or password incorrect"
);
}
// Authenticated; proceed
} finally {
try {
connection.close();
} catch (SQLException x) {
// Forward to handler
}
}
}
}
Noncompliant Code Example (PreparedStatement)
The JDBC library provides an API for building SQL commands that sanitize untrusted data. The java.sql.PreparedStatement class properly escapes input strings, preventing SQL injection when used correctly. This code example modifies the doPrivilegedAction() method to use a PreparedStatement instead of java.sql.Statement. However, the prepared statement still permits a SQL injection attack by incorporating the unsanitized input argument username into the prepared statement.
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
class Login {
public Connection getConnection() throws SQLException {
DriverManager.registerDriver(new
com.microsoft.sqlserver.jdbc.SQLServerDriver());
String dbConnection =
PropertyManager.getProperty("db.connection");
// Can hold some value like
// "jdbc:microsoft:sqlserver://<HOST>:1433,<UID>,<PWD>"
return DriverManager.getConnection(dbConnection);
}
String hashPassword(char[] password) {
// Create hash of password
}
public void doPrivilegedAction(
String username, char[] password
) throws SQLException {
Connection connection = getConnection();
if (connection == null) {
// Handle error
}
try {
String pwd = hashPassword(password);
String sqlString = "select * from db_user where username=" +
username + " and password =" + pwd;
PreparedStatement stmt = connection.prepareStatement(sqlString);
ResultSet rs = stmt.executeQuery();
if (!rs.next()) {
throw new SecurityException("User name or password incorrect");
}
// Authenticated; proceed
} finally {
try {
connection.close();
} catch (SQLException x) {
// Forward to handler
}
}
}
}
Compliant Solution (PreparedStatement)
This compliant solution uses a parametric query with a ꞌ?ꞌ character as a placeholder for the argument. This code also validates the length of the username argument, preventing an attacker from submitting an arbitrarily long user name.
public void doPrivilegedAction(
String username, char[] password
) throws SQLException {
Connection connection = getConnection();
if (connection == null) {
// Handle error
}
try {
String pwd = hashPassword(password);
// Validate username length
if (username.length() > 8) {
// Handle error
}
String sqlString =
"select * from db_user where username=? and password=?";
PreparedStatement stmt = connection.prepareStatement(sqlString);
stmt.setString(1, username);
stmt.setString(2, pwd);
ResultSet rs = stmt.executeQuery();
if (!rs.next()) {
throw new SecurityException("User name or password incorrect");
}
// Authenticated; proceed
} finally {
try {
connection.close();
} catch (SQLException x) {
// Forward to handler
}
}
}
Use the set*() methods of the PreparedStatement class to enforce strong type checking. This technique mitigates the SQL injection vulnerability because the input is properly escaped by automatic entrapment within double quotes. Note that prepared statements must be used even with queries that insert data into the database.
Risk Assessment
Failure to sanitize user input before processing or storing it can result in injection attacks.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
IDS00-J | High | Probable | Medium | P12 | L1 |
Automated Detection
| Tool | Version | Checker | Description |
|---|---|---|---|
| Coverity | 7.5 | SQLI FB.SQL_PREPARED_STATEMENT_GENERATED_ | Implemented |
| Findbugs | 1.0 | SQL_NONCONSTANT_STRING_PASSED_TO_EXECUTE | Implemented |
| Fortify | 1.0 | HTTP_Response_Splitting | Implemented |
| Klocwork | SV.DATA.BOUND | Implemented |
Related Vulnerabilities
CVE-2008-2370 describes a vulnerability in Apache Tomcat 4.1.0 through 4.1.37, 5.5.0 through 5.5.26, and 6.0.0 through 6.0.16. When a RequestDispatcher is used, Tomcat performs path normalization before removing the query string from the URI, which allows remote attackers to conduct directory traversal attacks and read arbitrary files via a .. (dot dot) in a request parameter.
Related Guidelines
| CERT Perl Coding Standard | IDS33-PL. Sanitize untrusted data passed across a trust boundary |
Injection [RST] | |
CWE-116, Improper encoding or escaping of output |
Android Implementation Details
This rule uses MS SQL Server as an example to show a database connection. However, on Android, DatabaseHelper from SQLite is used for a database connection. Because Android apps may receive untrusted data via network connections, the rule is applicable.
Bibliography
A Guide to Building Secure Web Applications and Web Services | |
| [Seacord 2015] | |
[W3C 2008] | 4.4.3, "Included If Validating" |
Rule 00: Input Validation and Data Sanitization (IDS) Rule 00: Input Validation and Data Sanitization (IDS)