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Chapter 10 ASP.NET Security

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  1. Chapter 10ASP.NET Security Yingcai Xiao

  2. Introduction to Web SecurityCategoriesIssuesComponents

  3. Building a Secure Web Site • Three Categories of Web Security: • Content freely available to everyone (public). • Serve the general population but require a login (application-level security, protected). • Intranet sites for a controlled population of users — a company’s employees (private). • Security Issues: • Application-level security (users). • Deployment security (programmers). • Web Security Components: • Authentication identifies the originator of requests (who). • Authorization defines who can access which pages (what).

  4. Authentication • ASP.NET supports three types of authentication: • Forms (Page-wide) • Windows (Machine-wide) • Passport (Internet-wide) • None • Web.config <configuration>  <system.web>      <authentication mode="Forms"/>   </system.web> </configuration> Note: • The authentication mode is an application-wide setting that can be set only in the application root and can’t be overridden in subordinate Web.config files. • You can’t use Windows authentication in one part of an application and forms authentication in another.

  5. Setting authentication mode in the root Web.config

  6. Authorization • ASP.NET supports two forms of authorization: • ACL (access control list) authorization, also known as file authorization, based on file system permissions, typically used with Windows authentication. • URL authorization, relies on configuration directives in Web.config files, most often used with forms authentication.

  7. Three Typical Security Scenarios for Web Applications • Pages can be freely browsed by any: no application-level security • Intranet application: use Windows authentication and ACL authorization. • Internet application with secure page access: use forms authentication and URL authorization.

  8. The Internal Working of IIS and ASP.NET Security

  9. IIS Security • IIS (Internet Information Services) Server • a Web server • runs in process Inetinfo.exe as SYSTEM • accepts connections • responds to HTTP requests • Web applications are deployed in application directories. Remote clients can’t arbitrarily grab files outside virtual directories. • IIS assigns every request an access token representing a Windows security principal. The access token enables the operating system to perform ACL checks on resources targeted. • IIS supports IP address and domain name restrictions. • IIS supports encrypted HTTP connections using the Secure Sockets Layer (SSL) family of protocols.

  10. IIS Security • Anonymous access (access by unauthenticated users) • Request from anonymous users are tagged with IUSR_machinename’s access token. IUSR_machinename is an Internet guest account created when IIS is installed, where machinename is usually the Web server’s machine name.

  11. ASP.NET Security • Server Side Processing: (1) Client accesses .ASPX files => (2)Inetinfo.exe (IIS) generates an access token =>Aspnet_isapi.dll sents the request and the token through named pipe or local procedure calls (LPCs) => (3) Aspnet_wp.exe (ASP.NET) makes ACL checks on the requested resource and passes access token to the targeted application => (4) Targeted application uses a HTTP pipeline => HTTP modules => HTTP handlers (mapped in Machine.config).

  12. The relationship between IIS and ASP.NET.

  13. Two types of access tokens: • Authenticated user: authenticated security principal • Unauthenticated user: IUSR_machinename for anonymous login • Start->Settings->Control Panel->Administrative Tools->Computer Management->Local Users and Groups->Users • Start->Settings->Control Panel->Administrative Tools->Computer Management->Event Viewer->Security

  14. The ASPNET Account • Created when ASP.NET is installed. • A member of the “Users” group. • Aspnet_wp.exe runs as ASPNET by default. • Requests executed by ASP.NET use Aspnet_wp.exe’s identity. • ASP.NET can impersonate to use the request’s access token. • To make Aspnet_wp.exe to run as SYSTEM, change processModel in Machine.config to <processModel userName="SYSTEM" ... />

  15. Impersonation • To execute a request using the access token provided by IIS. • Add the following in Web.config <identity impersonate="true" /> • The identities assigned to the ASP.NET worker process and to the requests that it executes play crucial roles.

  16. Programming Forms Authentication

  17. Forms Authentication • Forms authentication allows applications to setupweb authentications independently from the authentications of the operating systems. It works well with URL authorization, which relies on configuration directives in Web.config files. • Forms/URL security is useful to protect an e-commerce site (an external/Internet application for servicing customs of a company).

  18. Forms Authentication: Static Structure • Security settings in an ASP.NET-based web application are configured in the Web.config files. • The Web.config file in the root directory (which must be an application directory) specifies the authentication mode, application-specific login page. • The Web.config file in a subdirectory sets the authorization specifics for the directory. • User credentials can be stored in a database (preferred) or in the root Web.config file.

  19. Forms Authentication : Dynamic Behavior • The first time a user accesses a protected resource, ASP.NET redirects the user to the login page. • If the login is successful, ASP.NET then issues the user an authentication ticket in the form of a cookie (cookies need to be enabled by the client) and redirects the user to the page originally requested. • The ticket allows that user to revisit protected portions without having to login again. • The ticket’s lifetime can be controlled to determine how long the login is good for.

  20. A First Look at Forms Authentication • Forms1 Web Application • T:\Xiao\Windows Programming\Examples\C10\Forms1 • At the application root • PublicPage.aspx can be viewed by anyone • Web.config • LoginPage.aspx • In the Secret subdirectory • ProtectedPage.aspx is available only to authenticated users (wp/wp). • Web.config

  21. Deploy Forms1 on Winserv1 • Create a web application directory. C:\inetpub\wwwroot\VD\xiaotest\Forms1 You need to have admin privilege. On winserv1, use an existing web application directories already created for you, i.g., wppa5. • Copy everything from T:\Xiao\Windows Programming\Examples\C10\Forms1 to the above directory (C:\inetpub\wwwroot\VD\xiaotest\Forms1) • http://winserv1.cs.uakron.edu/VD/xiaotest/Forms1/PublicPage.aspx can be viewed by everyone. • http://winserv1.cs.uakron.edu/VD/xiaotest/Forms1/Secret/ProtectedPage.aspx is available only to authenticated users (wp/wp). • “Authenticated users” means anyone who has successfully logged in through LoginPage.aspx. • Valid users are stored in Web.config. • The cookie containing the authentication ticket is a session cookie, destroyed when the browser is closed. • You are not prompted for password again during a session.

  22. Programming Forms Security • Authentication in the root Web.config <authentication mode="Forms">   <forms loginUrl="LoginPage.aspx"> <credentials passwordFormat="Clear">   <user name="wp" password=“wp"/>  <user name="John" password="redrover" /> • Authorization (directory-wise) in Secret/Web.config <authorization>   <deny users="?" /> URL authorization to deny “?” (anonymous) users.

  23. Programming Forms Security • PublicPage.aspx void OnViewSecret (Object sender, EventArgs e)    { Response.Redirect ("Secret/ProtectedPage.aspx"); } • LoginPage.aspx. void OnLogIn (Object sender, EventArgs e)   { if(FormsAuthentication.Authenticate(UserName.Text,  Password.Text))      FormsAuthentication.RedirectFromLoginPage (UserName.Text, false); // “true” for persistent cookie       else Output.Text = "Invalid login";   } System.Web.Security.FormsAuthentication.Authentic method returns true if the user name and password are in the credentials section of Web.config.

  24. Internal Works • ASP.NET creates an authentication cookie, attaches it to the outgoing response, and redirects the user to the page that he or she originally requested. The lifetime of a persistent cookie is independent of the browser session. • Authorization is applied on a directory-by-directory basis. Web.config files in each directory specify exactly how the files are to be protected. • ASP.NET checks to see whether a valid authentication cookie is attached to the request. If the cookie exists, ASP.NET extracts identity information. If the cookie doesn’t exist, ASP.NET redirects the request to the login page.

  25. Real-World Forms Authentication – (Forms2) • Storing user names and passwords in a database (MySQL). • Creating the database, creating the “users” table and adding users. • Logo on to winserv1. • Start->All Programs->My SQL->My SQL Query Browser. • Server Host: db1.cs.uakron.edu • Port 3306 • Username: yourLoginID_wp • Password: yourPassword for MySQL • Default Schema: yourLoginID_wp • File->Open Script: T:\Xiao\Windows Programming\Examples\C10\MySQL-Table-Creation\Weblogin.sql • Execute!

  26. Real-World Forms Authentication Weblogin.sql CREATE TABLE users ( username varchar(32) NOT NULL, password varchar(32) NOT NULL, role varchar(32) ); INSERT INTO users (username, password, role) VALUES (‘dev', ‘dev', 'Developer'); INSERT INTO users (username, password, role) VALUES (‘mgr', ‘mgr', 'Manager'); … AddUsers.sql • INSERT INTO users (username, password, role) VALUES ('wpd1', 'wp2009', 'Developer'); • INSERT INTO users (username, password, role) VALUES ('wpd2', 'wp2009', 'Developer'); …

  27. Real-World Forms Authentication – (Forms2) • To deploy the application copy T:\Xiao\Windows Programming\Examples\C10\Forms2 to C:\Inetpub\wwwroot Create a “Forms2” virtual directory for it. • To access • http://localhost/Forms2/PublicPage.aspx can be viewed by anyone. • http://localhost/Forms2/Secret/ProtectedPage.aspx is available only to authenticated users (wpd1/wpd1).

  28. Deploy Forms2 on Winserv1 • Create a web application directory. C:\inetpub\wwwroot\VD\xiaotest\Forms2 You need to have admin privilege. On winserv1, use an existing web application directories already created for you, i.g., wppa5. • Copy everything from T:\Xiao\Windows Programming\Examples\C10\Forms2 to the above directory (C:\inetpub\wwwroot\VD\xiaotest\Forms2) • http://winserv1.cs.uakron.edu/VD/xiaotest/Forms2/PublicPage.aspx can be viewed by everyone. • http://winserv1.cs.uakron.edu/VD/xiaotest/Forms2/Secret/ProtectedPage.aspx is available only to authenticated users (wp/wp). • “Authenticated users” means anyone who has successfully logged in through LoginPage.aspx. • Valid users are stored in Web.config. • The cookie containing the authentication ticket is a session cookie, destroyed when the browser is closed. • You are not prompted for password again during a session.

  29. Real-World Forms Authentication LoginPage.aspx • Credential Matching: SQL: select count(*) from users where username = ‘dev' and pwd = ‘dev’;  It returns 0 if no matching credentials found. • MySQL notes: (1) count (*) works for SQL Server but not MySQL due to the extra space after count. (2) password is a keyword in MySQL (not SQL Server), therefore can’t be used as database column names. (3) ExecuteScalar returns Int64 for “count” query. • FormsAuthentication.RedirectFromLoginPage (UserName.Text, Persistent.Checked); Persistent authentication cookie: be able to get back without logging in again, even after shutting down.

  30. Authentication Cookie Lifetime • Session authentication cookie. Machine.config <forms ... timeout="30"> // 30 minutes Web.config <forms loginUrl="LoginPage.aspx" timeout="10080" /> // 7 days • Proramming cookies. HttpCookie cookie = Response.Cookies[FormsAuthentication.FormsCookieName]; cookie.Expires = DateTime.Now + new TimeSpan (7, 0, 0, 0); // 7 days • Removing cookies IE->Tools->Internet Options->General->Delete Cookies. Netscape->Tools->Cookie Manager->Manage stored cookies->Remove all. FireFox->Tools->Clear Private Data->Cookies->

  31. Forms AuthenticationRole-Based Security

  32. Forms Authentication and Role-Based Security (Forms3) • Use role membership to allow only some authenticated users to view Secret/ProtectedPage.aspx. • Without roles: Deny all unauthenticated users. <deny users="?" /> Deny all users (users=“*”) except John and Alice. <allow users="John, Alice" />       <deny users="*" /> Allow all except Jeff, Bob, and Mary: <deny users="Jeff, Bob, Mary" />       <allow users="*" /> <allow> and <deny> are order-sensitive. ASP.NET will stop at <…= “*”> and ignore any statements that appear after it.

  33. Forms Authentication and Role-Based Security (Forms3) • With roles: • “Users” table has a field named “role” that stores each user’s role (group) membership. • Grant Developer access to Secret. <allow roles="Developer" />      <deny users="*" /> • Map the roles to user accounts so that ASP.NET can determine whether the requestor is a developer or not. • Place the mapping in the AuthenticateRequest event handler (invoked at the beginning of every request). • Can be done in a custom HTTP module or in Global.asax. http://winserv1.cs.uakron.edu/VD/xiaotest/Forms3/PublicPage.aspx dev/dev/Developer can view ProtectedPage.aspx. mgr/mgr/Manager can’t.

  34. Programming Role-based Authentication • Getting Information about Authenticated Users in Your Code • ASP.NET stores user information in the HttpContext.User property. • Access User through Page.Context.User or simply Page.User, or HttpApplication.User. • The “User” property is of the type IPrincipal (an interface defined in System.Security.Principal). • Implemented by the WindowsPrincipal class for Windows authentication and GenericPrincipal class for other forms of authentication (along with Windows authentication). • GenericPrincipal is a device for representing user identities independent of the authentication protocol being used. ASP.NET compares the role name in the GenericPrincipal to the roles granted access through Web.config. • User.Identity contains some usefull properties:

  35. Properties in User.Identity if (User.Identity.IsAuthenticated) { string name = User.Identity.Name; … } Name is of the form domain-name\user-name for Windows authentication, user-typed login for forms authentication.

  36. Programming Authentication - Roles Retrieve a user’s role and create a Principal for the user. <%@ Import Namespace="System.Security.Principal" %> <script language="C#" runat="server"> • void Application_AuthenticateRequest (Object sender, EventArgs e) • { • HttpApplication app = (HttpApplication) sender; • if (app.Request.IsAuthenticated && • app.User.Identity is FormsIdentity) { • FormsIdentity identity = (FormsIdentity) app.User.Identity; • // Find out what role (if any) the user belongs to • string role = GetUserRole (identity.Name); • // Create a GenericPrincipal containing the role name • // and assign it to the current request • if (role != null) • app.Context.User = new GenericPrincipal (identity, • new string[] { role }); • } • }

  37. Programming Authentication - Roles string GetUserRole (string name) { MySqlConnection connection = new MySqlConnection ("server=db1.cs.uakron.edu;database=xiaotest;uid=xiaotest;pwd=wp2009; allow zero datetime=yes“) try { connection.Open (); StringBuilder builder = new StringBuilder (); builder.Append ("select role from users " + "where username = \'"); builder.Append (name); builder.Append ("\'"); MySqlCommand command = new MySqlCommand (builder.ToString (), connection); object role = command.ExecuteScalar (); if (role is DBNull) return null; return (string) role; } catch (MySqlException) { return null; } finally { connection.Close ();} }

  38. More on Forms Authentication • Multiple Roles Coding: app.Context.User = new GenericPrincipal (identity, new string[] { "Developer", "Manager" }); Web.config <allow roles="Manager, Developer" /> <deny users="*" /> • Configure subdirectories in root Web.config <location path="Secret"> <system.web> <authorization> <allow roles=" Developer" /> <deny users="*" /> </authorization> </system.web> </location>

  39. More on Forms Authentication • Signing Out <asp:Button Text="Log Out" OnClick="OnLogOut" RunAt="server" /> <script language="C#" runat="server"> void OnLogOut (Object sender, EventArgs e) { FormsAuthentication.SignOut (); } FormsAuthentication.SignOut( ): returns a Set-Cookie header, sets the cookie’s value to a null string and sets the cookie’s expiration date to a date in the past.

  40. More on Forms Authentication Attributes of forms element in Web.config: The protection attributes specifies the desired level of protection for the authentication cookies. “All” instructs ASP.NET to both encrypt and validate authentication cookies.

  41. Encrypt and Validate Authentication Cookies • Validation works by appending the machineKey element’s validationKey to the cookie, the resulting value is hashed, and the hash is appended to the cookie. When the cookie is returned in a request, ASP.NET verifies that it wasn’t tampered with by rehashing the cookie and comparing the new hash to the one accompanying the cookie. • Encryption works by encrypting the cookie—hash value and all—with machineKey’s decryptionKey attribute.

  42. Encrypt and Validate Authentication Cookies • Validation consumes less CPU time than encryption and prevents tampering. It does not prevent someone from intercepting an authentication cookie and reading its contents. • To validate but not encrypt authentication cookies: <forms ... protection="Validation" /> • Encryption provides insurance against tampering and prevents the cookie’s contents being read. • To encrypt but not validate cookies: <forms ... protection="Encryption " />

  43. Encrypt and Validate Authentication Cookies • To disable both: <forms ... protection="None" /> • Encrypted cookies can’t be read or altered, but can be stolen and used illicitly. Time-outs are the only protection. • The most reliable way to prevent someone from spoofing your site with a stolen authentication cookie is to use an encrypted communications link (HTTPS). • <forms ... loginUrl="https://www.wintellect.com/login.aspx" /> This assumes the server supports HTTPS and Login.aspx is stored in a directory configured to use HTTPS. • Caveat Emptor: ASP.NET does not protect HTML pages. Just renaming .html to .aspx to protect it. • http://winserv1.cs.uakron.edu/VD/xiaotest/Forms3/PublicPage.aspx • http://winserv1.cs.uakron.edu/VD/xiaotest/Forms3/Secret/ProtectedPage.aspx • http://winserv1.cs.uakron.edu/VD/xiaotest/Forms3/Secret/Calc.html • http://winserv1.cs.uakron.edu/VD/xiaotest/Forms3/Secret/Calc.aspx

  44. Windows Authentication

  45. Windows Authentication • It maps incoming requests to accounts on the Web server or in the Web server’s domain. Use it to serve content to a well-defined populace. • Don’t use it to generically expose content to all comers over the Internet. • Windows authentication on the front end is typically paired with ACL authorization (administrator controlled) on the back end. • Can be also used with URL authorization (programmer controlled).

  46. Windows Authentication • Categories of Windows Authentication: • Basic authentication: login, piggyback on HTTP. • Digest authentication: login, piggyback on HTTP. • Integrated Windows authentication: Windows login. • SSL client certificates: limited primarily to intranet.

  47. Basic Authentication • An HTTP standard (documented in RFC 2617, ftp://ftp.isi.edu/in-notes/rfc2617.txt.) • How it works: • For the first time access, the Web server returns a 401 status code indicating what type of authentication is required. • HTTP/1.1 401 Access Denied Server: Microsoft IIS-5.0  .  .  .WWW-Authenticate: Basic realm="uakron.edu" • A realm is a logical security space that encompasses all or part of a web site. • The browser pops up a dialog box asking for a user name and password.

  48. Basic Authentication • It concatenates the user name and password to an encoded string in the Authorization header of an HTTP request. Authorization: Basic SmVmZjppbWJhdG1hbg== • The browser includes the same Authorization header in each future request to the same realm. • IIS maps the user name and password to an account on the web server, producing an access token. • The access token is used to perform ACL-based security checks.

  49. Basic Authentication • Pros of Basic Authentication: • It works with virtually all browsers. • Easy to use. • It works well with firewalls. • Cons of Basic Authentication: • Nothing prevents requests from being intercepted and used to gain access to your server. • Some users consider pop-up dialogs intrusive. • Better to be used with HTTPS, not HTTP.

  50. Digest Authentication • Documented in RFC 2617 (ftp://ftp.isi.edu/in-notes/rfc2617.txt). • Similar to basic authentication. • The browser solicits a user name and password by popping up a dialog box. The server uses the credentials to assign an identity to the request. • The big difference between basic and digest authentication is that digest doesn’t transmit clear-text passwords. Instead, it passes an authentication token that is cryptographically secure. As a result, you can use it over unencrypted channels without fear of compromising your Web server.