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Difference between revisions of "Testing for Bypassing Authentication Schema (OTG-AUTHN-004)"

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== Summary ==
 +
 
 +
While most applications require authentication to gain access to private information or to execute tasks, not every authentication method is able to provide adequate security. Negligence, ignorance, or simple understatement of security threats often result in authentication schemes that can be bypassed by simply skipping the log in page and directly calling an internal page that is supposed to be accessed only after authentication has been performed.
 +
 
 +
 
 +
In addition, it is often possible to bypass authentication measures by tampering with requests and tricking the application into thinking that the user is already authenticated.  This can be accomplished either by modifying the given URL parameter, by manipulating the form, or by counterfeiting sessions.
 +
 
 +
 
 +
Problems related to the authentication schema can be found at different stages of the software development life cycle (SDLC), like the design, development, and deployment phases:
 +
* In the design phase errors can include a wrong definition of application sections to be protected, the choice of not applying strong encryption protocols for securing the transmission of credentials, and many more.
 +
* In the development phase errors can include the incorrect implementation of input validation functionality or not following the security best practices for the specific language.
 +
* In the application deployment phase, there may be issues during the application setup (installation and configuration activities) due to a lack in required technical skills or due to the lack of good documentation.
 +
 
 +
 
 +
== How to Test ==
 +
=== Black Box testing ===
 +
There are several methods of bypassing the authentication schema that is used by a web application:
 +
* Direct page request ([[Forced_browsing|forced browsing]])
 +
* Parameter modification
 +
* Session ID prediction
 +
* SQL injection
  
== Brief Summary ==
 
<br>
 
While most most application require authentication for gaining access to private information or tasks, not every authentication method is able to provide adequate security level.<br><br>
 
Negligence, ignorance or simple understatement of the security threats often result in authentication schemes that can be easily bypassed by simply skipping the login page and directly calling an internal page that is supposed to be accessed only after authentication has been performed.<br><br>
 
In addition to this it is often possible to bypass compulsory authentication tampering with requests and tricking the application into thinking that we're already authenticated either by modifying the given URL parameter or by manipulating form or by counterfeiting sessions.
 
 
<br>
 
<br>
 +
====Direct page request====
 +
 +
If a web application implements access control only on the log in page, the authentication schema could be bypassed.  For example, if a user directly requests a different page via forced browsing, that page may not check the credentials of the user before granting access. Attempt to directly access a protected page through the address bar in your browser to test using this method.
 +
 +
 +
<center>[[Image:basm-directreq.jpg]]</center>
 +
 +
 +
====Parameter Modification====
 +
 +
Another problem related to authentication design is when the application verifies a successful log in on the basis of a fixed value parameters. A user could modify these parameters to gain access to the protected areas without providing valid credentials. In the example below, the "authenticated" parameter is changed to a value of "yes", which allows the user to gain access.  In this example, the parameter is in the URL, but a proxy could also be used to modify the parameter, especially when the parameters are sent as form elements in a POST request or when the parameters are stored in a cookie.
 +
 +
<pre>http://www.site.com/page.asp?authenticated=no </pre>
 +
 +
<pre>[email protected] /home $nc www.site.com 80                   
 +
GET /page.asp?authenticated=yes HTTP/1.0                   
 +
                                                           
 +
HTTP/1.1 200 OK                                           
 +
Date: Sat, 11 Nov 2006 10:22:44 GMT                       
 +
Server: Apache                                             
 +
Connection: close                                         
 +
Content-Type: text/html; charset=iso-8859-1               
 +
 +
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">         
 +
<HTML><HEAD>                                               
 +
</HEAD><BODY>                                             
 +
<H1>You Are Authenticated</H1>                             
 +
</BODY></HTML>
 +
</pre>
 +
 +
<center>[[Image:basm-parammod.jpg]]</center>
 +
 +
 +
====Session ID Prediction====
 +
 +
Many web applications manage authentication by using session identifiers (session IDs). Therefore, if session ID generation is predictable, a malicious user could be able to find a valid session ID and gain unauthorized access to the application, impersonating a previously authenticated user.
 +
 +
 +
In the following figure, values inside cookies increase linearly, so it could be easy for an attacker to guess a valid session ID.
 +
 +
 +
<center>[[Image:basm-sessid.jpg]]</center>
 +
 +
 +
In the following figure, values inside cookies change only partially, so it's possible to restrict a brute force attack to the defined fields shown below.
 +
 +
 +
<center>[[Image:basm-sessid2.jpg]]</center>
 +
 +
 +
====SQL Injection (HTML Form Authentication)====
 +
 +
SQL Injection is a widely known attack technique. This section is not going to describe this technique in detail as there are several sections in this guide that explain injection techniques beyond the scope of this section.
  
== Description of the Issue ==
 
<br>
 
Problems related to Authentication Schema could be found at different stages of software development life cycle (SDLC), like design, development and deployment phase.
 
  
Examples of design errors include a wrong definition of application parts to be protected, the choice of not applying strong encryption protocols for securing authentication data exchange, and many more.
+
<center>[[Image:basm-sqlinj.jpg]]</center>
  
Problems in development phase are for example the incorrect implementation of input validation functionalities, or not following the security best practices for the specific language.
 
  
In addition there are issues during application setup (Installation and configuration activities) due to a lack in required technical skills, or due to poor documentation available.
+
The following figure shows that with a simple SQL injection attack, it is sometimes possible to bypass the authentication form.
<br>
 
  
== Black Box testing and example ==
 
There are several methods to bypass the authentication schema in use by a web application:
 
* Direct page request
 
* Parameter Modification
 
* Session ID Prediction
 
* Session Fixation
 
* Sql Injection
 
  
=== Bypassing authentication schema methods ===
+
<center>[[Image:basm-sqlinj2.gif]]</center>
  
'''Direct page request'''
 
  
[[Image:basm-directreq.jpg]]
+
=== Gray Box Testing ===
  
In alcuni casi la richiesta di autenticazione della web application avviene solamente quando si cerca di accedere alla home page, mentre se si accedede  a qualche risorsa richiamandola  direttamente si puo' bypassare lo schem di autenticazione
+
If an attacker has been able to retrieve the application source code by exploiting a previously discovered vulnerability (e.g., directory traversal), or from a web repository (Open Source Applications), it could be possible to perform refined attacks against the implementation of the authentication process.
  
'''Parameter Modification'''
 
  
[[Image:basm-parammod.jpg]]
+
In the following example (PHPBB 2.0.13 - Authentication Bypass Vulnerability), at line 5 the unserialize() function parses a user supplied cookie and sets values inside the $row array. At line 10 the user's MD5 password hash stored inside the back end database is compared to the one supplied.  
  
In alcuni casi l'autenticazione si basa sul valore con cui sono impostati alcuni parametri quindi e' sufficiente modificarli per bypassare lo schema di autenticazione
+
<pre>
 +
1.  if ( isset($HTTP_COOKIE_VARS[$cookiename . '_sid']) ||
 +
2.  {
 +
3.  $sessiondata = isset( $HTTP_COOKIE_VARS[$cookiename . '_data'] ) ?
 +
4.
 +
5.  unserialize(stripslashes($HTTP_COOKIE_VARS[$cookiename . '_data'])) : array();
 +
6.
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7.  $sessionmethod = SESSION_METHOD_COOKIE;
 +
8.  }
 +
9.
 +
10. if( md5($password) == $row['user_password'] && $row['user_active'] )
 +
11.
 +
12. {
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13. $autologin = ( isset($HTTP_POST_VARS['autologin']) ) ? TRUE : 0;
 +
14. }
 +
</pre>
  
For example, /webapps/login?validUser=yes&isAutheticated=yes can be manually entered into the browser in an attempt to bypass the application server's authentication mechanism.
 
  
'''Session Issue'''
+
In PHP, a comparison between a string value and a boolean value (1 - "TRUE") is always "TRUE", so by supplying the following string (the important part is "b:1") to the unserialize() function, it is possible to bypass the authentication control:
* Session ID Prediction
 
* Session Fixation
 
 
 
'''Sql Injection (HTML Form Authentication)'''
 
  
 +
a:2:{s:11:"autologinid";b:1;s:6:"userid";s:1:"2";}
  
[[Image:basm-sqlinj.jpg]]
 
  
[[Image:basm-sqlinj2.gif]]
+
==Tools==
 +
* [[OWASP WebScarab Project|WebScarab]]
 +
* [[OWASP WebGoat Project|WebGoat]]
 +
* [https://www.owasp.org/index.php/OWASP_Zed_Attack_Proxy_Project OWASP Zed Attack Proxy (ZAP)]
  
<br>
 
  
== Gray Box testing and example ==
 
'''Testing for Topic X vulnerabilities:'''<br>
 
...<br>
 
'''Result Expected:'''<br>
 
...<br><br>
 
 
== References ==
 
== References ==
 
'''Whitepapers'''<br>
 
'''Whitepapers'''<br>
...<br>
+
* Mark Roxberry: "PHPBB 2.0.13 vulnerability"
'''Tools'''<br>
+
* David Endler: "Session ID Brute Force Exploitation and Prediction" - http://www.cgisecurity.com/lib/SessionIDs.pdf
...<br>
 
 
 
{{Category:OWASP Testing Project AoC}}
 
[[OWASP Testing Guide v2 Table of Contents]]
 
{{Template:Stub}}
 

Latest revision as of 14:44, 5 August 2014

This article is part of the new OWASP Testing Guide v4.
Back to the OWASP Testing Guide v4 ToC: https://www.owasp.org/index.php/OWASP_Testing_Guide_v4_Table_of_Contents Back to the OWASP Testing Guide Project: https://www.owasp.org/index.php/OWASP_Testing_Project

Summary

While most applications require authentication to gain access to private information or to execute tasks, not every authentication method is able to provide adequate security. Negligence, ignorance, or simple understatement of security threats often result in authentication schemes that can be bypassed by simply skipping the log in page and directly calling an internal page that is supposed to be accessed only after authentication has been performed.


In addition, it is often possible to bypass authentication measures by tampering with requests and tricking the application into thinking that the user is already authenticated. This can be accomplished either by modifying the given URL parameter, by manipulating the form, or by counterfeiting sessions.


Problems related to the authentication schema can be found at different stages of the software development life cycle (SDLC), like the design, development, and deployment phases:

  • In the design phase errors can include a wrong definition of application sections to be protected, the choice of not applying strong encryption protocols for securing the transmission of credentials, and many more.
  • In the development phase errors can include the incorrect implementation of input validation functionality or not following the security best practices for the specific language.
  • In the application deployment phase, there may be issues during the application setup (installation and configuration activities) due to a lack in required technical skills or due to the lack of good documentation.


How to Test

Black Box testing

There are several methods of bypassing the authentication schema that is used by a web application:

  • Direct page request (forced browsing)
  • Parameter modification
  • Session ID prediction
  • SQL injection


Direct page request

If a web application implements access control only on the log in page, the authentication schema could be bypassed. For example, if a user directly requests a different page via forced browsing, that page may not check the credentials of the user before granting access. Attempt to directly access a protected page through the address bar in your browser to test using this method.


Basm-directreq.jpg


Parameter Modification

Another problem related to authentication design is when the application verifies a successful log in on the basis of a fixed value parameters. A user could modify these parameters to gain access to the protected areas without providing valid credentials. In the example below, the "authenticated" parameter is changed to a value of "yes", which allows the user to gain access. In this example, the parameter is in the URL, but a proxy could also be used to modify the parameter, especially when the parameters are sent as form elements in a POST request or when the parameters are stored in a cookie.

http://www.site.com/page.asp?authenticated=no 
[email protected] /home $nc www.site.com 80                    
GET /page.asp?authenticated=yes HTTP/1.0                    
                                                            
HTTP/1.1 200 OK                                             
Date: Sat, 11 Nov 2006 10:22:44 GMT                         
Server: Apache                                              
Connection: close                                           
Content-Type: text/html; charset=iso-8859-1                 
 
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">          
<HTML><HEAD>                                                
</HEAD><BODY>                                               
<H1>You Are Authenticated</H1>                              
</BODY></HTML>
Basm-parammod.jpg


Session ID Prediction

Many web applications manage authentication by using session identifiers (session IDs). Therefore, if session ID generation is predictable, a malicious user could be able to find a valid session ID and gain unauthorized access to the application, impersonating a previously authenticated user.


In the following figure, values inside cookies increase linearly, so it could be easy for an attacker to guess a valid session ID.


Basm-sessid.jpg


In the following figure, values inside cookies change only partially, so it's possible to restrict a brute force attack to the defined fields shown below.


Basm-sessid2.jpg


SQL Injection (HTML Form Authentication)

SQL Injection is a widely known attack technique. This section is not going to describe this technique in detail as there are several sections in this guide that explain injection techniques beyond the scope of this section.


Basm-sqlinj.jpg


The following figure shows that with a simple SQL injection attack, it is sometimes possible to bypass the authentication form.


Basm-sqlinj2.gif


Gray Box Testing

If an attacker has been able to retrieve the application source code by exploiting a previously discovered vulnerability (e.g., directory traversal), or from a web repository (Open Source Applications), it could be possible to perform refined attacks against the implementation of the authentication process.


In the following example (PHPBB 2.0.13 - Authentication Bypass Vulnerability), at line 5 the unserialize() function parses a user supplied cookie and sets values inside the $row array. At line 10 the user's MD5 password hash stored inside the back end database is compared to the one supplied.

1.  if ( isset($HTTP_COOKIE_VARS[$cookiename . '_sid']) ||
2.  {
3.  $sessiondata = isset( $HTTP_COOKIE_VARS[$cookiename . '_data'] ) ?
4. 
5.  unserialize(stripslashes($HTTP_COOKIE_VARS[$cookiename . '_data'])) : array();
6. 
7.  $sessionmethod = SESSION_METHOD_COOKIE;
8.  }
9. 
10. if( md5($password) == $row['user_password'] && $row['user_active'] )
11. 
12. {
13. $autologin = ( isset($HTTP_POST_VARS['autologin']) ) ? TRUE : 0;
14. }


In PHP, a comparison between a string value and a boolean value (1 - "TRUE") is always "TRUE", so by supplying the following string (the important part is "b:1") to the unserialize() function, it is possible to bypass the authentication control:

a:2:{s:11:"autologinid";b:1;s:6:"userid";s:1:"2";}


Tools


References

Whitepapers