CA2100: Review SQL queries for security vulnerabilities

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TypeName ReviewSqlQueriesForSecurityVulnerabilities
CheckId CA2100
Category Microsoft.Security
Breaking Change Non-breaking

Cause

A method sets the System.Data.IDbCommand.CommandText property by using a string that is built from a string argument to the method.

Rule Description

This rule assumes that the string argument contains user input. A SQL command string that is built from user input is vulnerable to SQL injection attacks. In a SQL injection attack, a malicious user supplies input that alters the design of a query in an attempt to damage or gain unauthorized access to the underlying database. Typical techniques include injection of a single quotation mark or apostrophe, which is the SQL literal string delimiter; two dashes, which signifies a SQL comment; and a semicolon, which indicates that a new command follows. If user input must be part of the query, use one of the following, listed in order of effectiveness, to reduce the risk of attack.

int x = 10;
string query = "SELECT TOP " + x.ToString() + " FROM Table";

The rule is violated because a malicious user can override the ToString() method.

The rule also is violated when ToString is used implicitly.

int x = 10;
string query = String.Format("SELECT TOP {0} FROM Table", x);

How to Fix Violations

To fix a violation of this rule, use a parameterized query.

When to Suppress Warnings

It is safe to suppress a warning from this rule if the command text does not contain any user input.

Example

The following example shows a method, UnsafeQuery, that violates the rule and a method, SaferQuery, that satisfies the rule by using a parameterized command string.

#using <System.dll>
#using <System.Data.dll>
#using <System.EnterpriseServices.dll>
#using <System.Transactions.dll>
#using <System.Xml.dll>
using namespace System;
using namespace System::Data;
using namespace System::Data::SqlClient;

namespace SecurityLibrary
{
   public ref class SqlQueries
   {
   public:
      Object^ UnsafeQuery(
         String^ connection, String^ name, String^ password)
      {
         SqlConnection^ someConnection = gcnew SqlConnection(connection);
         SqlCommand^ someCommand = gcnew SqlCommand();
         someCommand->Connection = someConnection;

         someCommand->CommandText = String::Concat(
            "SELECT AccountNumber FROM Users WHERE Username='", 
            name, "' AND Password='", password, "'");

         someConnection->Open();
         Object^ accountNumber = someCommand->ExecuteScalar();
         someConnection->Close();
         return accountNumber;
      }

      Object^ SaferQuery(
         String^ connection, String^ name, String^ password)
      {
         SqlConnection^ someConnection = gcnew SqlConnection(connection);
         SqlCommand^ someCommand = gcnew SqlCommand();
         someCommand->Connection = someConnection;

         someCommand->Parameters->Add(
            "@username", SqlDbType::NChar)->Value = name;
         someCommand->Parameters->Add(
            "@password", SqlDbType::NChar)->Value = password;
         someCommand->CommandText = "SELECT AccountNumber FROM Users "  
            "WHERE Username=@username AND Password=@password";

         someConnection->Open();
         Object^ accountNumber = someCommand->ExecuteScalar();
         someConnection->Close();
         return accountNumber;
      }
   };
}

using namespace SecurityLibrary;

void main()
{
   SqlQueries^ queries = gcnew SqlQueries();
   queries->UnsafeQuery(Environment::GetCommandLineArgs()[1], 
      "' OR 1=1 --", "anything");
   // Resultant query (which is always true): 
   // SELECT AccountNumber FROM Users WHERE Username='' OR 1=1

   queries->SaferQuery(Environment::GetCommandLineArgs()[1], 
      "' OR 1 = 1 --", "anything");
   // Resultant query (notice the additional single quote character):
   // SELECT AccountNumber FROM Users WHERE Username=''' OR 1=1 --'
   //                                   AND Password='anything'
}
using System;
using System.Data;
using System.Data.SqlClient;

namespace SecurityLibrary
{
   public class SqlQueries
   {
      public object UnsafeQuery(
         string connection, string name, string password)
      {
         SqlConnection someConnection = new SqlConnection(connection);
         SqlCommand someCommand = new SqlCommand();
         someCommand.Connection = someConnection;

         someCommand.CommandText = "SELECT AccountNumber FROM Users " +
            "WHERE Username='" + name + 
            "' AND Password='" + password + "'";

         someConnection.Open();
         object accountNumber = someCommand.ExecuteScalar();
         someConnection.Close();
         return accountNumber;
      }

      public object SaferQuery(
         string connection, string name, string password)
      {
         SqlConnection someConnection = new SqlConnection(connection);
         SqlCommand someCommand = new SqlCommand();
         someCommand.Connection = someConnection;

         someCommand.Parameters.Add(
            "@username", SqlDbType.NChar).Value = name;
         someCommand.Parameters.Add(
            "@password", SqlDbType.NChar).Value = password;
         someCommand.CommandText = "SELECT AccountNumber FROM Users " + 
            "WHERE Username=@username AND Password=@password";

         someConnection.Open();
         object accountNumber = someCommand.ExecuteScalar();
         someConnection.Close();
         return accountNumber;
      }
   }

   class MalaciousCode
   {
      static void Main(string[] args)
      {
         SqlQueries queries = new SqlQueries();
         queries.UnsafeQuery(args[0], "' OR 1=1 --", "anything");
         // Resultant query (which is always true): 
         // SELECT AccountNumber FROM Users WHERE Username='' OR 1=1

         queries.SaferQuery(args[0], "' OR 1 = 1 --", "anything");
         // Resultant query (notice the additional single quote character):
         // SELECT AccountNumber FROM Users WHERE Username=''' OR 1=1 --'
         //                                   AND Password='anything'
      }
   }
}
Imports System
Imports System.Data
Imports System.Data.SqlClient

Namespace SecurityLibrary

   Public Class SqlQueries

      Function UnsafeQuery(connection As String, _ 
         name As String, password As String) As Object
      
         Dim someConnection As New SqlConnection(connection)
         Dim someCommand As New SqlCommand()
         someCommand.Connection = someConnection

         someCommand.CommandText = "SELECT AccountNumber FROM Users " & _ 
            "WHERE Username='" & name & "' AND Password='" & password & "'"

         someConnection.Open()
         Dim accountNumber As Object = someCommand.ExecuteScalar()
         someConnection.Close()
         Return accountNumber

      End Function

      Function SaferQuery(connection As String, _ 
         name As String, password As String) As Object
      
         Dim someConnection As New SqlConnection(connection)
         Dim someCommand As New SqlCommand()
         someCommand.Connection = someConnection

         someCommand.Parameters.Add( _ 
            "@username", SqlDbType.NChar).Value = name
         someCommand.Parameters.Add( _ 
            "@password", SqlDbType.NChar).Value = password
         someCommand.CommandText = "SELECT AccountNumber FROM Users " & _  
            "WHERE Username=@username AND Password=@password"

         someConnection.Open()
         Dim accountNumber As Object = someCommand.ExecuteScalar()
         someConnection.Close()
         Return accountNumber

      End Function

   End Class 

   Class MalaciousCode

      Shared Sub Main(args As String())
      
         Dim queries As New SqlQueries()
         queries.UnsafeQuery(args(0), "' OR 1=1 --", "anything")
         ' Resultant query (which is always true): 
         ' SELECT AccountNumber FROM Users WHERE Username='' OR 1=1

         queries.SaferQuery(args(0), "' OR 1 = 1 --", "anything")
         ' Resultant query (notice the additional single quote character):
         ' SELECT AccountNumber FROM Users WHERE Username=''' OR 1=1 --' 
         '                                   AND Password='anything'
      End Sub

   End Class

End Namespace

See Also

Security Overview