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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 [email protected].
Development
Deployment
Fetch the Latest Files
The latest Stinger release can be downloaded [TBD here]. The deployer 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:
<filter> <filter-name>StingerFilter</filter-name> <filter-class>org.owasp.stinger.StingerFilter</filter-class> <init-param> <param-name>config</param-name> <param-value>C:\stinger.xml</param-value> </init-param> <init-param> <param-name>errmsg</param-name> <param-value>A serious error has occurred</param-value> </init-param> <init-param> <param-name>reload</param-name> <param-value>true</param-value> </init-param> </filter>
Stinger 2.0 accepts three filter parameters: config, errmsg, and reload. The config parameter tells the Stinger filter the location of the SVDL file. The errmsg parameter is actually the result of a new feature in Stinger 2.0. 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 writes a message to the client upon catching an exception. The errmsg parameter specifies the message that will be displayed to the user. 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> <filter-name>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.
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
- errmsg - the error message 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 [email protected].
AbstractAction
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 {
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 doAction(Violation violation, MutableHttpRequest request,
MutableHttpResponse response) throws BreakChainException;
}
ClearCookies
Description
As the name implies, the ClearCookies action will set the maximum age of every cookie in the request to 0; effectively clearing all cookies for the session.
Parameters
The ClearCookies action currently does not accept any parameters.
Source Code
public class ClearCookies extends AbstractAction {
public void doAction(Violation violation, MutableHttpRequest request, MutableHttpResponse response) {
Cookie[] cookies = null;
cookies = request.getCookies();
if(cookies != null) {
for(int i=0; i<cookies.length; i++) {
cookies[i].setMaxAge(0);
}
}
}
}
DisplayMessage
Description
When a violation occurs, the DisplayMessage action can be configured to display a custom message to the user. This message currently resides at the top of the response in an HTML table format.
Parameters
The DisplayMessage action currently accepts two parameters.
message - the message to be displayed back to the user upon finding a violation
bgcolor - the background color of the HTML table
Source Code
public class DisplayMessage extends AbstractAction {
public String formatMessage(String message, String bgcolor) {
StringBuffer buffer = new StringBuffer();
buffer.append("<table width=300 border=1 align=center bgcolor=" + bgcolor + " cellpadding=2\n");
buffer.append("<tr><td>\n");
buffer.append("<div align=\"center\" >" + message + "</div>\n");
buffer.append("</td></tr></table>\n");
return buffer.toString();
}
public void displayMessage(MutableHttpResponse response, String message, String bgcolor) {
PrintWriter out = null;
String formatedMessage = formatMessage(message, bgcolor);
out = response.getWriter();
out.write(formatedMessage);
}
public void doAction(Violation violation, MutableHttpRequest request, MutableHttpResponse response) {
String message = getParameter("message");
String bgcolor = getParameter("bgcolor");
displayMessage(response, message, bgcolor);
}
}
Drop
Description
The Drop action simply throws the BreakChainException when called. This effectively prevents the HTTP request from ever reaching the web application.
Parameters
The Drop action currently accepts one parameter:
message - the message to be displayed in the exception stack trace. This message is never displayed to the user.
Source Code
public class Drop extends AbstractAction {
public void doAction(Violation violation, MutableHttpRequest request,
MutableHttpResponse response) throws BreakChainException {
String message = getParameter("message");
/** Let the user define the message to be displayed in the exception **/
throw new BreakChainException(message);
}
}
Invalidate
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 doAction(Violation violation, MutableHttpRequest request, MutableHttpResponse response) {
HttpSession session = null;
session = request.getSession(false);
if(session != null) {
session.invalidate();
}
}
}
Log
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, and the JSESSIONID. The format strings are %ip, %port, %name, %value, %js respectively.
Source Code
public class Log extends AbstractAction {
private static Logger logger = Logger.getLogger("org.owasp.stinger.actions.Log");
private static HashMap<String, FileHandler> handlers = new HashMap<String, FileHandler>();
public Log() {
}
public void doAction(Violation violation, MutableHttpRequest request, MutableHttpResponse response) {
FileHandler handler = null;
String log = getParameter("log");
String level = getParameter("level");
String message = getParameter("message");
/** 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");
}
/** Offender's JSESSIONID **/
if(request.getCookie("JSESSIONID") != null) {
message = message.replace("%js", request.getCookie("JSESSIONID").getValue());
} else {
message = message.replace("%js", "NULL");
}
handler = getHandler(log);
logger.addHandler(handler);
logger.log(Level.parse(level.toUpperCase()), message);
handler.flush();
logger.removeHandler(handler);
}
private synchronized FileHandler getHandler(String log) {
FileHandler handler = null;
handler = handlers.get(log);
if(handler == null) {
try {
handler = new FileHandler(log);
} catch (IOException ioe) {
ioe.printStackTrace();
}
handlers.put(log, handler);
}
return handler;
}
}
Redirect
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 {
public void doAction(Violation violation, MutableHttpRequest request,
MutableHttpResponse response) throws BreakChainException {
String page = getParameter("page");
try {
response.sendRedirect(page);
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
}
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!
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Project Sponsors
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