OWASP Stinger Manual

=Overview=

The purpose of the OWASP Stinger manual is to provide users a comprehensive guide to developing upon and deploying the OWASP J2EE Stinger filter. If you have any comments or suggestions concerning the Stinger manual, please to not hesitate to email me at [mailto:eric.sheridan@owasp.org eric.sheridan@owasp.org].

=Development=

=Deployment=

Fetch the Latest Files
The latest Stinger release can be downloaded here. The user implementing Stinger should download the jar file into a directory accessible by the Java container. For example, deploying Stinger in Tomcat would require downloading the files in the WEB-INF/lib/ directory.

Configure Deployment Descriptor
There are two major pieces of information necessary to deploy Stinger in your J2EE environment. First, the Java container must be told to implement the Stinger J2EE filter. This is specified in the web.xml file via the following:

StingerFilter org.owasp.stinger.StingerFilter  config stinger.xml   error-page fatal-error.html   reload</param-name> false</param-value> </init-param>

Stinger 2.x accepts three filter parameters: config, error-page, and reload. The config parameter tells the Stinger filter the location of the SVDL file. The error-page parameter is actually the result of a new feature in Stinger 2.x. All exceptions that are thrown from the web application are now caught in Stinger. This prevents sending exceptions to the client and potentially revealing sensitive information (think database exceptions). Instead of leaking sensitive information, Stinger simply redirects the client to a specified page upon catching an exception. The third parameter, reload, tells Stinger whether to dynamically load the SVDL file for each incoming HTTP request. As a rule of thumb, set reload to true in testing environments and false for production environments.

The second major piece of information dictates which requests should pass the Stinger J2EE filter. This is specified in the web.xml file via the following:

<filter-mapping> StingerFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>

This entry tells the J2EE container that every request handled by the container should pass through the Stinger filter.

Configure Your SVDL File
A template SVDL file for the latest Stinger release can be found here. The SVDL file is broken down into three sections.


 * The Regular Expression Section
 * The Cookie Rule Section
 * The Parameter Rule Section

The Regular Expression Section
All regular expressions to be used in Stinger are defined in this section. Essentially, a regular expression entry is comprised of a name, a regular expression, and a description. The description element is for user readability and is not used within Stinger. The regular expressions equiped with Stinger were taken from the OWASP RegEx Repository. If you have custom regular expressions and would like to donate them to the Stinger project, please email me at [mailto:eric.sheridan@owasp.org eric.sheridan@owasp.org].

The following is a sample entry in the regular expression section:

JSESSIONID ^[A-F0-9]{32}$ JSESSIONID character and length enforcement

The Cookie Rule Section
This section contains definitions for all of the cookies for which we are assigning a rule. A cookie rule is comprised of a name, a regular expression, the URI in which it is created, the URI's which it is enforced, and the actions taken if the cookie is missing or malformed. For most web applications, we wish to create and enforce a cookie for a particular URI. In this case, we have an entry similar to the one found below. In this case the following rule applies: ''if a cookie is missing from the request sent to the created/enforced URI, then no violation occurs. However, if a cookies is malformed in the request sent to the created/enforced URI, then a violation occurs.''

The missing and malformed sections simply specify the severity of the violation as well as the actions to be executed. There exists three possible severities: FATAL, CONTINUE, and IGNORE.


 * If a severity is FATAL, then Stinger stops processing the packet and immediately executes the associated actions.
 * If a severity is CONTINUE, then Stinger appends the violation a list and continues to process the packet.
 * If a severity is IGNORE, no violation is appended to the list of violation and Stinger continues its request validation.

Several actions accept parameters which are designated by the tag.

The following is a sample entry in the cookie rule section:

JSESSIONID JSESSIONID /Stinger-2.2.* /Stinger-2.2.* FATAL <action class="org.owasp.stinger.actions.Log"> log default.log level SEVERE message The required JSESSIONID cookie is missing <action class="org.owasp.stinger.actions.Invalidate" /> <action class="org.owasp.stinger.actions.Redirect"> page error.html FATAL <action class="org.owasp.stinger.actions.Log"> log default.log level SEVERE message The JSESSIONID cookie is malformed <action class="org.owasp.stinger.actions.Invalidate" /> <action class="org.owasp.stinger.actions.Redirect"> page error.html

The Parameter Section
The parameter section describes the parameter rules associated with a particular URI. A URI and its associated rules constitute a rule set. Every SVDL implementation must contain a default rule set similar to the following:

STINGER_DEFAULT STINGER_DEFAULT STINGER_ALL safetext ignore continue <action class="org.owasp.stinger.actions.Log"> log default.log level info message parameter %name with value %encoded_value from %ip has been encoded <action class="org.owasp.stinger.actions.Encode" />

A default Stinger rule set must have the path (the URI) set to STINGER_DEFAULT and the rule name set to STINGER_ALL. When a request to a URI without an associated rule set is submitted, the default rule set is utilized. When a parameter without an associated rule is sent to the application, then the default rules are utilized.

The following is a sample rule set entry for a fictitious web application:

Main /Stinger-2.2.* username safetext continue continue <action class="org.owasp.stinger.actions.Log"> log default.log level info message The username parameter from %ip is malformed <action class="org.owasp.stinger.actions.Encode" /> hidden1 safetext fatal <action class="org.owasp.stinger.actions.Log"> log default.log level info message The hidden1 parameter is missing <action class="org.owasp.stinger.actions.Invalidate" /> <action class="org.owasp.stinger.actions.Redirect"> page error.html fatal <action class="org.owasp.stinger.actions.Log"> log default.log level SEVERE message hidden1 parameter from %ip is malformed <action class="org.owasp.stinger.actions.Invalidate" /> <action class="org.owasp.stinger.actions.Redirect"> page error.html

Although this entry is quite large, there are only a few new entries which must be noted. As we see, this rule set utilizes a regular expression which is intended to cover the following URIs:


 * /Stinger-2.4
 * /Stinger-2.4/
 * /Stinger-2.4/index.jsp.

For this rule set, we have specified two rules, each describing a parameter accepted by the web application. These two parameters, username and hidden1, have very similar entries to that of the cookie rules. Each parameter has an associated regular expression, a missing section, and a malformed section.

Important SVDL Rules/Guidelines
When creating your own SVDL file, please remember the following rules/guidelines:

Defaults:
 * 1) Stinger assumes there will always exist a default rule set
 * 2) Requested URI's without a rule set will use the default rule set
 * 3) Parameters without an associated rule will use the default rule

Cookies:
 * 1) You must specify a created page for a cookie rule
 * 2) If a cookie is missing on the created page, then no violation
 * 3) If a cookie is malformed on the created page, then violation
 * 4) You must specify at least one enforced uri per cookie rule
 * 5) You can specify more than one enforced uri per cookie rule

Rule Sets:
 * 1) There must exist at least one path per rule set.
 * 2) There can exist multiple paths for a single rule set.

Actions:
 * 1) Order actions carefully and appropriately. Ex. You cannot drop a packet and then display a message.
 * 2) Several actions accept parameters. They must be defined

SVDL Learner Filter
A project is underway to create a J2EE filter which generates an SVDL file based on captured HTTP traffic. The learner filter will behave similar to that of the SVDL Generator filter whereby parameters without an associated rule will be colored red. The learner filter will then look for a user-submitted value for that parameter and build an appropriate rule with default missing and malformed actions. When the user is finished crawling the site, the J2EE container is shut down and the Learner filter writes the rules to disk. The learner filter is considered developmental, yet it is included in the Stinger 2.x releases.

Deployment Checklist

 * Download the latest Stinger jar files into the appropriate container directory
 * Configure your web.xml file to:
 * Load Stinger with the appropriate parameters:
 * config - the location of the SVDL file under WEB-INF
 * error-page - the error page displayed if any exception is caught
 * reload - specifies whether the SVDL should be dynamically loaded at runtime
 * Apply Stinger to a URI Pattern


 * Configure the SVDL for your application

=Actions=

Stinger is an action based input validation engine. The user can specify actions to be taken place upon violations found in an HTTP request. The following section describes how the actions are implemented as well as the parameters they accept. One major goal of this section is to illustrate the simplicity of creating Stinger actions. If you have created a custom action and are interested in submitting it to the Stinger project, please email me at [mailto:eric.sheridan@owasp.org eric.sheridan@owasp.org].

Description
Developing your own action is relatively straight forward within Stinger. To implement a custom class, simply extend the AbstractAction class and implement the abstract doAction method. For more information related to building custom actions, please refer to the development section.

Source Code
public abstract class AbstractAction { public final static int DROP = -1; public final static int CONTINUE = 0; public final static int PROCESS = 1; private HashMap<String, String> parameters = new HashMap<String, String>; public String getParameter(String name) { return parameters.get(name); } 	public void setParameter(String name, String value) { parameters.remove(name); parameters.put(name, value); } 	public abstract void init(ServletContext context); public abstract int doAction(Violation violation, MutableHttpRequest request, HttpServletResponse response); }

Description
The Drop action simply DROP when called. This effectively prevents the HTTP request from ever reaching the web application.

Parameters
The Drop action currently accepts zero parameters:

Source Code
public class Drop extends AbstractAction { public void init(ServletContext context) { } 	public int doAction(Violation violation, MutableHttpRequest request, HttpServletResponse response) { return DROP; } }

Description
If the session object exists, then it will be invalidated by this action. This action is considered more severe and should be deployed only when an obvious attack occurs. For example, cookie values are rarely tampered with by the client side code (i.e. javascript). Therefore, we can (safely?) assume that any cookie modification is considered a deliberate attack.

Parameters
The Invalidate action currently accepts no parameters.

Source Code
public class Invalidate extends AbstractAction { public void init(ServletContext context) { } 	public int doAction(Violation violation, MutableHttpRequest request, HttpServletResponse response) { HttpSession session = request.getSession(false); if(session != null) { session.invalidate; } Cookie cookie = new Cookie("JSESSIONID", ""); cookie.setMaxAge(0); response.addCookie(cookie); return CONTINUE; } }

Description
As the name implies, we can log any and every request sent to the web application. The Log action is an essential action and should be heavily implemented in Stinger deployment.

Parameters
The Log action currently accepts 3 parameters:

log - the log file where the message should be recorded

level - the level of the log message (i.e. INFO, SEVERE, etc.)

message - the message which shall be logged. The message parameter itself accepts 3 format parameters. These include the offender's ip address, the offender's remote port, the parameter/cookie name, the parameter/cookie value, an entity encoded version of the parameter/cookie value, and the JSESSIONID. The format strings are %ip, %port, %name, %value, %encoded_value, and %js respectively. limit - the limit of the log file size count - the maximum number of log files to use append - specifies append mode (true/false)

Source Code
public class Log extends AbstractAction { private static Logger logger = Logger.getLogger("org.owasp.stinger.actions.Log"); private static FileHandler handler = null; private ServletContext context = null; public Log { } 	public void init(ServletContext context) { this.context = context; } 	public int doAction(Violation violation, MutableHttpRequest request, HttpServletResponse response) { String log = getParameter("log"); String level = getParameter("level"); String message = getParameter("message"); String limit = getParameter("limit"); String count = getParameter("count"); String append = getParameter("append"); if(handler == null) { getHandler(log, limit, count, append); } 		/** Offender's IP **/ message = message.replace("%ip", request.getRemoteAddr); /** Offender's Port **/ message = message.replace("%port", String.valueOf(request.getRemotePort)); /** Offending parameter name **/ if(violation.getName != null) { message = message.replace("%name", violation.getName); } else { message = message.replace("%name", "NULL"); } 		/** Offending parameter value **/ if(violation.getValue != null) { message = message.replace("%value", violation.getValue); } else { message = message.replace("%value", "NULL"); } 		/** Offending parameter value HTML Encoded **/ if(violation.getValue != null) { message = message.replace("%encoded_value", violation.getValue); } else { message = message.replace("%encoded_value", "NULL"); } 		/** Offender's JSESSIONID (HASHED) **/ if(request.getCookie("JSESSIONID") != null) { String s = request.getCookie("JSESSIONID").getValue; byte[] b = null; try { b = CryptoUtil.doWeakHash(s.getBytes); } catch (CryptoException e) { context.log("[Stinger-Filter] caught crypto exception in doAction", e); } 			message = message.replace("%js", Encoder.BASE64Encode(b)); } else { message = message.replace("%js", "NULL"); } 		logger.log(new LogRecord(Level.parse(level.toUpperCase), message)); return CONTINUE; } 	private synchronized void getHandler(String log, String limit, String count, String append) { int l = -1; int c = -1; boolean a = false; try { l = Integer.parseInt(limit); } catch (NumberFormatException e) { context.log("[Stinger-Filter] getHandler: " + l + " is not a valid int, defaulting to " +   (1024*1024)); l = 1024*1024; } 		try { c = Integer.parseInt(count); } catch (NumberFormatException e) { context.log("[Stinger-Filter] getHandler: " + count + " is not a valid int, defaulting to 1"); c = 1; } 		a = Boolean.parseBoolean(append); getHandler(log, l, c, a); } 	private synchronized void getHandler(String log, int limit, int count, boolean append) { try { if(handler == null) { handler = new FileHandler(log, limit, count, append); } 		} catch (IOException ioe) { context.log("[Stinger-Filter] exception in getHandler", ioe); } 	} }

Description
The Redirect action redirects a user to a specific page. This action is often used to send a user to an error message upon finding a violation.

Parameters
The Redirect action currently accepts 1 parameter:

page - the page to redirect the user to

Source Code
public class Redirect extends AbstractAction { private ServletContext context = null; public void init(ServletContext context) { this.context = context; } 	public int doAction(Violation violation, MutableHttpRequest request, HttpServletResponse response) { String page = getParameter("page"); try { response.sendRedirect(page); } catch (IOException ioe) { context.log("[Stinger-Filter] caught exception during redirect", ioe); } 		return PROCESS; } }

Description
The Forward action Forwards users request to a specific page for processing.

Parameters
The Forward action currently accepts 1 parameter:

page - the page to forward the user to

Source Code
public class Forward extends AbstractAction { private ServletContext context = null; public void init(ServletContext context) { this.context = context; } 	public int doAction(Violation violation, MutableHttpRequest request, HttpServletResponse response) { String page = getParameter("page"); try { request.getRequestDispatcher(page).forward(request, response); } catch (IOException ioe) { context.log("[Stinger-Filter] exception in doAction", ioe); } catch (ServletException se) { context.log("[Stinger-Filter] exception in doAction", se); } 		return PROCESS; } }

Description
The encode action will HTML Entity Encode the violating value. This effectively prevents cross site scripting from the violating input value.

Source Code
public class Encode extends AbstractAction { private void entityEncode(MutableHttpRequest request, String name, String value) { String result = null; if(value != null) { result = Encoder.HTMLEntityEncode(value); request.addParameter(name, result); } 	} 	public void init(ServletContext context) { } 	public int doAction(Violation violation, MutableHttpRequest request, HttpServletResponse response) { String name = null; String value = null; name = violation.getName; value = request.getParameter(name); entityEncode(request, name, value); return CONTINUE; } } =Example SVDL Configuration Files=

The following are example SVDL configuration files. With the introduction of the global rules concept, configuring Stinger becomes significantly less cumbersome for even the most complex apps.

Template SVDL File
This configuration should be used as a template for creating your own SVDL files. It contains a basic regular expression section, a basic cookie section, and no parameter rules.

Click here to download this template SVDL file.

Encode all Input
This SVDL configuration encodes all parameters in the HTTP request. By entity encoding all parameter-based user input, we significantly reduce the likelihood of certain forms of Cross Site Scripting and SQL Injection attacks.

Click here to download this sample SVDL file.

Encode all Input and Log All Violations
This SVDL configuration encodes all parameters in the HTTP request and logs all violations that may occur. As a result, we significantly reduce the likelihood of certain input validation attacks and we have a logging mechanism to detect and verifies these attacks.

Click here to download this sample SVDL file.

Encode all Input for a Particular URI
This SVDL configuration encodes all parameters in the HTTP request that are sent to a specific set of URI's. If a malformed parameter is sent to another URI not listed in our rule, then the global rule handles the packet. Since the global rule does nothing, the malformed data will be accepted.

Click here to download this sample SVDL file.

=Feedback and Participation =

We hope you find Stinger useful. Please contribute back to the project by sending your comments, questions, and suggestions to the Stinger mailing list. Thanks!

To join the OWASP Stinger mailing list or view the archives, please visit the subscription page.

=Project Sponsors=

The Stinger project is sponsored by http://www.owasp.org/images/d/d1/Aspect_logo.gif.