| # Apache Tomcat 6.0 Version 6.0.36, Oct 16 2012 |

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Table of Contents
Introduction CSRF Prevention Filter Introduction Filter Class Name Initialisation parameters Set Character Encoding Filter Introduction Filter Class Name Initialisation parameters Failed Request Filter Introduction Filter Class Name Initialisation parameters
Introduction
Tomcat provides a number of Filters which may be configured for use with all web applications using `$CATALINA_BASE/conf/web.xml` or may be configured for individual web applications by configuring them in the application's `WEB-INF/web.xml`. Each filter is described below. This description uses the variable name $CATALINA_BASE to refer the base directory against which most relative paths are resolved. If you have not configured Tomcat for multiple instances by setting a CATALINA_BASE directory, then $CATALINA_BASE will be set to the value of $CATALINA_HOME, the directory into which you have installed Tomcat.
CSRF Prevention Filter
> Introduction
> This filter provides basic CSRF protection for a web application. The filter assumes that it is mapped to `/*` and that all URLs returned to the client are encoded via a call to `HttpServletResponse#encodeRedirectURL(String)` or `HttpServletResponse#encodeURL(String)`. This filter prevents CSRF by generating a nonce and storing it in the session. URLs are also encoded with the same nonce. When the next request is received the nonce in the request is compared to the nonce in the session and only if they are the same is the request allowed to continue.
> Filter Class Name
> The filter class name for the CSRF Prevention Filter is `org.apache.catalina.filters.CsrfPreventionFilter` .
> Initialisation parameters
> > The CSRF Prevention Filter supports the following initialisation parameters:
> > Attribute | Description
> > --- | ---
> > `entryPoints` | A comma separated list of URLs that will not be tested for the presence of a valid nonce. They are used to provide a way to navigate back to a protected application after having navigated away from it. Entry points will be limited to HTTP GET requests and should not trigger any security sensitive actions.
> > `nonceCacheSize` | The number of previously issued nonces that will be cached on a LRU basis to support parallel requests, limited use of the refresh and back in the browser and similar behaviors that may result in the submission of a previous nonce rather than the current one. If not set, the default value of 5 will be used.
> > `randomClass` | The name of the class to use to generate nonces. The class must be an instance of `java.util.Random`. If not set, the default value of `java.security.SecureRandom` will be used.
Set Character Encoding Filter
> Introduction
> User agents don't always include character encoding information in requests. Depending on the how the request is processed, usually the default encoding of ISO-8859-1 is used. This is not always desirable. This filter provides options for setting that encoding or forcing it to a particular value. Essentially this filter calls `ServletRequest.setCharacterEncoding()` method. Effectively the value set by this filter is used when parsing parameters in a POST request, if parameter parsing occurs later than this filter. Thus the order of filter mappings is important. Note that the encoding for GET requests is not set here, but on a Connector. See CharacterEncoding page in the FAQ for details.
> Filter Class Name
> The filter class name for the Set Character Encoding Filter is `org.apache.catalina.filters.SetCharacterEncodingFilter`.
> Initialisation parameters
> > The Set Character Encoding Filter supports the following initialization parameters:
> > Attribute | Description
> > --- | ---
> > `encoding` | Name of the character encoding which should be set.
> > `ignore` | Determines if any character encoding specified by the user agent is ignored. If this attribute is `true`, any value provided by the user agent is ignored. If `false`, the encoding is only set if the user agent did not specify an encoding. The default value is `false`.
Failed Request Filter
> Introduction
> This filter triggers parameters parsing in a request and rejects the request if some parameters were skipped during parameter parsing because of parsing errors or request size limitations (such as `maxParameterCount` attribute in a Connector). This filter can be used to ensure that none parameter values submitted by client are lost. Note that parameter parsing may consume the body of an HTTP request, so caution is needed if the servlet protected by this filter uses `request.getInputStream()` or `request.getReader()` calls. In general the risk of breaking a web application by adding this filter is not so high, because parameter parsing does check content type of the request before consuming the request body. Note, that for the POST requests to be parsed correctly, a `SetCharacterEncodingFilter` filter must be configured above this one. See CharacterEncoding page in the FAQ for details. The request is rejected with HTTP status code 400 (Bad Request).
> Filter Class Name
> The filter class name for the Failed Request Filter is `org.apache.catalina.filters.FailedRequestFilter`.
> Initialisation parameters
> The Failed Request Filter does not support any initialization parameters.
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