Effective Security in ASP.Net Applications

1
Effective Security in ASP.Net Applications

• Jatin Sharma

2
Types of Threats
Network
Host
Application
Threats against the network

Threats against the host
Threats against the application
3
Application Security

• Error handling
• Form authentication
• Input validation
• Data access data protection

4
Error Handling

• Use web.config to handle errorsThree different
  modes for customErrorsltcustomErrors
  modeRemoteOnly /gt
  or Off or
  On
• Off display detailed asp.net error information
• On display custom (friendly) messages.
• RemoteOnly no detailed error for remote clients.

5
Securing the site with error handling

• Example 1ltcustomErrors mode"On"
  defaultRedirect"error.aspx"/gt

6
Site Security

• By default, site users are anonymous.
• They may need to be authenticated and
  authorized.Authentication the process of
  verifying a users identity.Authorization to
  measure or establish the power or permission that
  has been given or granted by an authority.

7
ASP.Net Authentication

• 4 different modes of authentication.- Windows
  uses windows authentication system on the web
  server (for intranet).- Forms uses ASP.Net
  form-based authentication (for internet).-
  Passport uses Microsofts Passport
  Authentication- None no authentication.

8
Specifying Authentication Type

• Web.config

ltconfigurationgt ltsystem.webgt lt!--
mode"WindowsPassportFormsNone" --gt
ltauthentication mode"Windows" /gt
lt/system.webgt lt/configurationgt
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Forms Authentication Options
Web.config
ltconfigurationgt ltsystem.webgt
ltauthentication mode"Forms"gt lt!--
forms Attributes name"cookie name" -
Authentication cookie name
loginUrl"url" - URL of login page
protection"AllNoneEncryptionValidation"
timeout"minutes" - Length of time cookie
valid path"/" - Cookie path
requireSSL"truefalse" - Restrict cookie to
SSL? slidingExpiration"truefalse" -
Renew cookie? --gt lt/authenticationgt
lt/system.webgt lt/configurationgtSee Page 862.
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Authenticating Against the Web.Config file

• ltconfigurationgt
• ltsystem.webgt
• ltauthentication mode"Forms"gt
• ltforms name.MyCookie"
  loginUrlLogin.aspx
• protectionAll"
• timeout"15
• path"/" gt
• ltcredentials passwordFormatCleargt
  ltuser nameSam passwordSecret /gt
  ltuser nameFred passwordFred /gt
• lt/credentialsgt
• lt/formsgt
• lt/authenticationgt
• lt/system.webgt
• lt/configurationgt

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User Authorization
Web.config
lt!-- Deny access to anonymous (unauthenticated)
users --gt ltdeny users"?" /gt lt!-- Grant access
to Robin and Tim but no one else --gt ltallow
users"Bob, Alice" /gt ltdeny users"" /gt lt!--
Grant access to everyone EXCEPT Bob and Alice
--gt ltdeny usersRobin, Tim" /gt ltallow users""
/gt lt!-- Grant access to any manager --gt ltallow
roles"Manager" /gt ltdeny users"" /gt
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The Login Page

• First provide a namespace to the classes in the
  top of your class module as followsImports
  System.Web.Security

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The Login Page (cont.)
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Using the Authenticate() Method
Private Sub Button1_Click(ByVal sender As
System.Object, ByVal e As System.EventArgs)
Handles Button1.Click If FormsAuthentication.Aut
henticate(txtName.Text, txtPassword.Text) Then
FormsAuthentication.RedirectFromLoginPage
(txtName.Text, False) Else
lblMessage.Text "Bad Login" End IfEnd Sub
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Global.Asax

• protected void Application_AuthenticateRequest(Obj
  ect sender, EventArgs e)
• if (HttpContext.Current.User ! null)
• if (HttpContext.Current.User.Identity.IsA
  uthenticated)
• if (HttpContext.Current.
  User.Identity is FormsIdentity)
• // Get Forms Identity From
  Current User
• FormsIdentity id (FormsIdentity)HttpContext.
  Current.User.Identity
• // Get Forms Ticket From Identity object
• FormsAuthenticationTicket ticket id.Ticket
• // Retrieve stored user-data (our roles from
  db)
• string userData ticket.UserData
• string roles userData.Split(',')
• // Create a new Generic Principal Instance
  and assign to Current User

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The Authenticate() Method (cont.)

• The FormsAuthentication Object handles form
  security as specified in the Web.Config.
• RedirectFromLogin Page redirects to the requested
  page if the user has the permission.

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Authenticating Against a Database
cnn.Open() Dim i As Integer Dim
myCommand As New SqlClient.SqlCommand
myCommand.Connection cnn
myCommand.CommandText "select from userList
where uname'" _ txtName.Text "'
and upassword'" txtPassword.Text "'"
i myCommand.ExecuteScalar If i
gt 0 Then FormsAuthentication.RedirectF
romLoginPage(txtName.Text, False) Else
lblMessage.Text "Bad Login"
End If Cnn.Close() End Sub
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SQL Injection

• Exploits applications that use external input in
  database commands
• The technique
• Find a ltformgt field or query string parameter
  used to generate SQL commands
• Submit input that modifies the commands
• Compromise, corrupt, and destroy data

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How SQL Injection Works
Model Query
SELECT COUNT () FROM Users WHERE
UserNameJeff AND Passwordimbatman
Malicious Query
SELECT COUNT () FROM Users WHERE UserName or
11-- AND Password
"or 11" matches every record in the table
"--" comments out the remainder of the query
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Avoid SQL Injection

• Validation Control.
• SQL Stored Procedure.

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Accessing Data Securely
Use stored procedures
Never use sa to access Web databases
Store connection strings securely
Apply administrative protections to SQL Server
Optionally use SSL/TLS or IPSec to secure
the connection to the database server 2
22
The sa Account

• For administration only never use it to access a
  database programmatically
• Instead, use one or more accounts that have
  limited database permissions
• For queries, use SELECT-only account
• Better yet, use stored procs and grant account
  EXECUTE permission for the stored procs
• Reduces an attacker's ability to execute harmful
  commands (e.g., DROP TABLE)

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Creating a Limited Account
USE Login GO -- Add account named webuser to
Login database EXEC sp_addlogin 'webuser',
'mxyzptlk', 'Login' -- Grant webuser access to
the database EXEC sp_grantdbaccess 'webuser' --
Limit webuser to calling proc_IsUserValid GRANT
EXECUTE ON proc_IsUserValid TO webuser
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Connection Strings

• Storing plaintext database connection strings in
  Web.config is risky
• Vulnerable to file disclosure attacks
• Storing encrypted database connection strings
  increases security
• Encrypting connection strings is easy
• System.Security.Cryptography classes

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Database Passwords

• Encrypting
• string name FormsAuthentication.HashPasswordForS
  toringInConfigFile(TextBox2.Text,"MD5")
• Decrypting
• string pwd FormsAuthentication.HashPasswordForSt
  oringInConfigFile(TextBox2.Text,"MD5")
• string command "SELECT roles FROM users WHERE
  username '" TextBox1.Text "' AND pass '"
  pwd "'"