## Container Provided Filters

### Table of Contents

- Introduction
- Add Default Character Set Filter
  1. Introduction
  2. Filter Class Name
  3. Initialisation parameters
- CORS Filter
  1. Introduction
  2. Filter Class Name
  3. Initialisation parameters
  4. CORS Filter and HttpServletRequest attributes
- CSRF Prevention Filter
  1. Introduction
  2. Filter Class Name
  3. Initialisation parameters
- CSRF Prevention Filter for REST APIs
  1. Introduction
  2. Basic configuration sample
  3. RestCsrfPreventionFilter and HttpServletRequest parameters
  4. Filter Class Name
  5. Initialisation parameters
- Expires Filter
  1. Introduction
  2. Basic configuration sample
  3. Alternate Syntax
  4. Expiration headers generation eligibility
  5. Expiration configuration selection
  6. Filter Class Name
  7. Initialisation parameters
  8. Troubleshooting
- Failed Request Filter
  1. Introduction
  2. Filter Class Name
  3. Initialisation parameters
- HTTP Header Security Filter
  1. Introduction
  2. Filter Class Name
  3. Initialisation parameters
- Remote Address Filter
  1. Introduction
  2. Filter Class Name
  3. Initialisation parameters
  4. Example
- Remote Host Filter
  1. Introduction
  2. Filter Class Name
  3. Initialisation parameters
- Remote CIDR Filter
  1. Introduction
  2. Filter Class Name
  3. Initialisation parameters
  4. Example
- Remote IP Filter
  1. Introduction
  2. Filter Class Name
  3. Basic configuration to handle 'x-forwarded-for'
  4. Basic configuration to handle 'x-forwarded-for' and 'x-forwarded-proto'
  5. Advanced configuration with internal proxies
  6. Advanced configuration with trusted proxies
  7. Advanced configuration with internal and trusted proxies
  8. Advanced configuration with an untrusted proxy
  9. Initialisation parameters
- Request Dumper Filter
  1. Introduction
  2. Filter Class Name
  3. Initialisation parameters
  4. Sample Configuration
- Session Initializer Filter
  1. Introduction
  2. Filter Class Name
  3. Initialisation parameters
  4. Sample Configuration
- Set Character Encoding Filter
  1. Introduction
  2. Filter Class Name
  3. Initialisation parameters
- WebDAV Fix Filter
  1. Introduction
  2. Filter Class Name
  3. 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.

### Add Default Character Set Filter

#### Introduction

The HTTP specification is clear that if no character set is specified for media sub-types of the "text" media type, the ISO-8859-1 character set must be used. However, browsers may attempt to auto-detect the character set. This may be exploited by an attacker to perform an XSS attack. Internet Explorer and other browsers have an option to enable this behavior.

This filter prevents the attack by explicitly setting a character set. Unless the provided character set is explicitly overridden by the user the browser will adhere to the explicitly set character set, thus preventing the XSS attack.

#### Filter Class Name

The filter class name for the Add Default Character Set Filter is `org.apache.catalina.filters.AddDefaultCharsetFilter` .

#### Initialisation parameters

The Add Default Character Set Filter supports the following initialization parameters:

Attribute | Description
--- | ---
`encoding` | Name of the character set which should be set, if no other character set was set explicitly by a Servlet. This parameter has two special values `default` and `system`. A value of `system` uses the JVM wide default character set, which is usually set by locale. A value of `default` will use ISO-8859-1.

### CORS Filter

#### Introduction

This filter is an implementation of W3C's CORS (Cross-Origin Resource Sharing) specification, which is a mechanism that enables cross-origin requests.

The filter works by adding required `Access-Control-*` headers to HttpServletResponse object. The filter also protects against HTTP response splitting. If request is invalid, or is not permitted, then request is rejected with HTTP status code 403 (Forbidden). A flowchart that demonstrates request processing by this filter is available.

The minimal configuration required to use this filter is:

    <filter>
      <filter-name>CorsFilter</filter-name>
      <filter-class>org.apache.catalina.filters.CorsFilter</filter-class>
    </filter>
    <filter-mapping>
      <filter-name>CorsFilter</filter-name>
      <url-pattern>/*</url-pattern>
    </filter-mapping>

The above configuration enables the filter but does not relax the cross-origin policy. As a minimum, you will need to add a cors.allowed.origins initialisation parameter as described below to enable cross-origin requests. Depending on your requirements, you may need to provide additional configuration.

An instance of this filter can only implement one policy. If you want to apply different policies (e.g. different allowed origins) to different URLs or sets of URLs within your web application you will need to configure a separate instance of this filter for each policy you wish to configure.

#### Filter Class Name

The filter class name for the CORS Filter is `org.apache.catalina.filters.CorsFilter`.

#### Initialisation parameters

The CORS Filter supports following initialisation parameters:

Attribute | Description
--- | ---
`cors.allowed.origins` | A list of origins that are allowed to access the resource. A `*` can be specified to enable access to resource from any origin. Otherwise, a whitelist of comma separated origins can be provided. Eg: `https://www.w3.org, https://www.apache.org`. Defaults: The empty String. (No origin is allowed to access the resource).
`cors.allowed.methods` | A comma separated list of HTTP methods that can be used to access the resource, using cross-origin requests. These are the methods which will also be included as part of `Access-Control-Allow-Methods` header in pre-flight response. Eg: `GET, POST`. Defaults: `GET, POST, HEAD, OPTIONS`
`cors.allowed.headers` | A comma separated list of request headers that can be used when making an actual request. These headers will also be returned as part of `Access-Control-Allow-Headers` header in a pre-flight response. Eg: `Origin,Accept`. Defaults: `Origin, Accept, X-Requested-With, Content-Type, Access-Control-Request-Method, Access-Control-Request-Headers`
`cors.exposed.headers` | A comma separated list of headers other than simple response headers that browsers are allowed to access. These are the headers which will also be included as part of `Access-Control-Expose-Headers` header in the pre-flight response. Eg: `X-CUSTOM-HEADER-PING,X-CUSTOM-HEADER-PONG`. Default: None. Non-simple headers are not exposed by default.
`cors.preflight.maxage` | The amount of seconds, browser is allowed to cache the result of the pre-flight request. This will be included as part of `Access-Control-Max-Age` header in the pre-flight response. A negative value will prevent CORS Filter from adding this response header to pre-flight response. Defaults: `1800`
`cors.support.credentials` | A flag that indicates whether the resource supports user credentials. This flag is exposed as part of `Access-Control-Allow-Credentials` header in a pre-flight response. It helps browser determine whether or not an actual request can be made using credentials. Defaults: `false`
`cors.request.decorate` | A flag to control if CORS specific attributes should be added to HttpServletRequest object or not. Defaults: `true`

Here's an example of a more advanced configuration, that overrides defaults:

    <filter>
      <filter-name>CorsFilter</filter-name>
      <filter-class>org.apache.catalina.filters.CorsFilter</filter-class>
      <init-param>
        <param-name>cors.allowed.origins</param-name>
        <param-value>https://www.apache.org</param-value>
      </init-param>
      <init-param>
        <param-name>cors.allowed.methods</param-name>
        <param-value>GET,POST,HEAD,OPTIONS,PUT</param-value>
      </init-param>
      <init-param>
        <param-name>cors.allowed.headers</param-name>
        <param-value>Content-Type,X-Requested-With,accept,Origin,Access-Control-Request-Method,Access-Control-Request-Headers</param-value>
      </init-param>
      <init-param>
        <param-name>cors.exposed.headers</param-name>
        <param-value>Access-Control-Allow-Origin,Access-Control-Allow-Credentials</param-value>
      </init-param>
      <init-param>
        <param-name>cors.support.credentials</param-name>
        <param-value>true</param-value>
      </init-param>
      <init-param>
        <param-name>cors.preflight.maxage</param-name>
        <param-value>10</param-value>
      </init-param>
    </filter>
    <filter-mapping>
      <filter-name>CorsFilter</filter-name>
      <url-pattern>/*</url-pattern>
    </filter-mapping>

#### CORS Filter and HttpServletRequest attributes

CORS Filter adds information about the request, in HttpServletRequest object, for consumption downstream. Following attributes are set, if `cors.request.decorate` initialisation parameter is `true`:

- cors.isCorsRequest: Flag to determine if request is a CORS request.
- cors.request.origin: The Origin URL, i.e. the URL of the page from where the request originated.
- cors.request.type: Type of CORS request. Possible values:
  - `SIMPLE`: A request which is not preceded by a pre-flight request.
  - `ACTUAL`: A request which is preceded by a pre-flight request.
  - `PRE_FLIGHT`: A pre-flight request.
  - `NOT_CORS`: A normal same-origin request.
  - `INVALID_CORS`: A cross-origin request, which is invalid.
- cors.request.headers: Request headers sent as `Access-Control-Request-Headers` header, for a pre-flight request.

### 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
--- | ---
`denyStatus` | HTTP response status code that is used when rejecting denied request. The default value is `403`.
`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.

### CSRF Prevention Filter for REST APIs

#### Introduction

This filter provides basic CSRF protection for REST APIs. The CSRF protection is applied only for modifying HTTP requests (different from GET, HEAD, OPTIONS) to protected resources. It is based on a custom header `X-CSRF-Token` that provides a valid nonce.

CSRF protection mechanism for REST APIs consists of the following steps:

- Client asks for a valid nonce. This is performed with a non-modifying "Fetch" request to protected resource.
- Server responds with a valid nonce mapped to the current user session.
- Client provides this nonce in the subsequent modifying requests in the frame of the same user session.
- Server rejects all modifying requests to protected resources that do not contain a valid nonce.

#### Basic configuration sample

On the server side

- All CSRF protected REST APIs should be protected with an authentication mechanism.
- Protect modifying REST APIs with this filter.
- Provide at least one non-modifying operation.

    <filter>
      <filter-name>RestCSRF</filter-name>
      <filter-class>org.apache.catalina.filters.RestCsrfPreventionFilter</filter-class>
    </filter>
    <filter-mapping>
      <filter-name>RestCSRF</filter-name>
      <!-- Modifying operations -->
      <url-pattern>/resources/removeResource</url-pattern>
      <url-pattern>/resources/addResource</url-pattern>
      <!-- Non-modifying operations -->
      <url-pattern>/resources/listResources</url-pattern>
    </filter-mapping>

On the client side

- Make a non-modifying "Fetch" request in order to obtain a valid nonce. This can be done with sending additional header `X-CSRF-Token: Fetch`
- Cache the returned session id and nonce in order to provide them in the subsequent modifying requests to protected resources.
- Modifying requests can be denied and header `X-CSRF-Token: Required` will be returned in case of invalid or missing nonce, expired session or in case the session id is changed by the server.

    Client Request:
    GET /rest/resources/listResources HTTP/1.1
    X-CSRF-Token: Fetch
    Authorization: Basic ...
    Host: localhost:8080
    ...

    Server Response:
    HTTP/1.1 200 OK
    Set-Cookie: JSESSIONID=...; Path=/rest; HttpOnly
    X-CSRF-Token: ...
    ...

    Client Request:
    POST /rest/resources/addResource HTTP/1.1
    Cookie: JSESSIONID=...
    X-CSRF-Token: ...
    Authorization: Basic ...
    Host: localhost:8080
    ...

    Server Response:
    HTTP/1.1 200 OK
    ...

#### RestCsrfPreventionFilter and HttpServletRequest parameters

When the client is not able to insert custom headers in its calls to REST APIs there is additional capability to configure URLs for which a valid nonce will be accepted as a request parameter.

Note: If there is a `X-CSRF-Token` header, it will be taken with preference over any parameter with the same name in the request. Request parameters cannot be used to fetch new nonce, only header can be used to request a new nonce.

    <filter>
      <filter-name>RestCSRF</filter-name>
      <filter-class>org.apache.catalina.filters.RestCsrfPreventionFilter</filter-class>
      <init-param>
        <param-name>pathsAcceptingParams</param-name>
        <param-value>/resources/removeResource,/resources/addResource</param-value>
      </init-param>
    </filter>
    <filter-mapping>
      <filter-name>RestCSRF</filter-name>
      <url-pattern>/resources/*</url-pattern>
    </filter-mapping>

#### Filter Class Name

The filter class name for the CSRF Prevention Filter for REST APIs is `org.apache.catalina.filters.RestCsrfPreventionFilter` .

#### Initialisation parameters

The CSRF Prevention Filter for REST APIs supports the following initialisation parameters:

Attribute | Description
--- | ---
`denyStatus` | HTTP response status code that is used when rejecting denied request. The default value is `403`.
`pathsAcceptingParams` | A comma separated list of URLs that can accept nonces via request parameter `X-CSRF-Token`. For use cases when a nonce information cannot be provided via header, one can provide it via request parameters. If there is a `X-CSRF-Token` header, it will be taken with preference over any parameter with the same name in the request. Request parameters cannot be used to fetch new nonce, only header can be used to request a new nonce.
`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.

### Expires Filter

#### Introduction

ExpiresFilter is a Java Servlet API port of Apache mod_expires. This filter controls the setting of the `Expires` HTTP header and the `max-age` directive of the `Cache-Control` HTTP header in server responses. The expiration date can set to be relative to either the time the source file was last modified, or to the time of the client access.

These HTTP headers are an instruction to the client about the document's validity and persistence. If cached, the document may be fetched from the cache rather than from the source until this time has passed. After that, the cache copy is considered "expired" and invalid, and a new copy must be obtained from the source.

To modify `Cache-Control` directives other than `max-age` (see RFC 2616 section 14.9), you can use other servlet filters or Apache Httpd mod_headers module.

#### Basic configuration sample

Basic configuration to add '`Expires`' and '`Cache-Control: max-age=`' headers to images, css and javascript.

    <filter>
     <filter-name>ExpiresFilter</filter-name>
     <filter-class>org.apache.catalina.filters.ExpiresFilter</filter-class>
     <init-param>
        <param-name>ExpiresByType image</param-name>
        <param-value>access plus 10 minutes</param-value>
     </init-param>
     <init-param>
        <param-name>ExpiresByType text/css</param-name>
        <param-value>access plus 10 minutes</param-value>
     </init-param>
     <init-param>
        <param-name>ExpiresByType application/javascript</param-name>
        <param-value>access plus 10 minutes</param-value>
     </init-param>
    </filter>
    ...
    <filter-mapping>
     <filter-name>ExpiresFilter</filter-name>
     <url-pattern>/*</url-pattern>
     <dispatcher>REQUEST</dispatcher>
    </filter-mapping>

#### Alternate Syntax

The `ExpiresDefault` and `ExpiresByType` directives can also be defined in a more readable syntax of the form:

    <init-param>
     <param-name>ExpiresDefault</param-name>
     <param-value><base> [plus] {<num> <type>}*</param-value>
    </init-param>

    <init-param>
     <param-name>ExpiresByType type</param-name>
     <param-value><base> [plus] {<num> <type>}*</param-value>
    </init-param>

    <init-param>
     <param-name>ExpiresByType type;encoding</param-name>
     <param-value><base> [plus] {<num> <type>}*</param-value>
    </init-param>

where `<base>` is one of:

- `access`
- `now` (equivalent to '`access`')
- `modification`

The `plus` keyword is optional. `<num>` should be an integer value (acceptable to `Integer.parseInt()`), and `<type>` is one of:

- `year`, `years`
- `month`, `months`
- `week`, `weeks`
- `day`, `days`
- `hour`, `hours`
- `minute`, `minutes`
- `second`, `seconds`

For example, any of the following directives can be used to make documents expire 1 month after being accessed, by default:

    <init-param>
     <param-name>ExpiresDefault</param-name>
     <param-value>access plus 1 month</param-value>
    </init-param>

    <init-param>
     <param-name>ExpiresDefault</param-name>
     <param-value>access plus 4 weeks</param-value>
    </init-param>

    <init-param>
     <param-name>ExpiresDefault</param-name>
     <param-value>access plus 30 days</param-value>
    </init-param>

The expiry time can be fine-tuned by adding several '`<num> <type>`' clauses:

    <init-param>
     <param-name>ExpiresByType text/html</param-name>
     <param-value>access plus 1 month 15 days 2 hours</param-value>
    </init-param>

    <init-param>
     <param-name>ExpiresByType image/gif</param-name>
     <param-value>modification plus 5 hours 3 minutes</param-value>
    </init-param>

Note that if you use a modification date based setting, the `Expires` header will not be added to content that does not come from a file on disk. This is due to the fact that there is no modification time for such content.

#### Expiration headers generation eligibility

A response is eligible to be enriched by `ExpiresFilter` if :

1. no expiration header is defined (`Expires` header or the `max-age` directive of the `Cache-Control` header),
2. the response status code is not excluded by the directive `ExpiresExcludedResponseStatusCodes`,
3. the `Content-Type` of the response matches one of the types defined the in `ExpiresByType` directives or the `ExpiresDefault` directive is defined.

Note : If `Cache-Control` header contains other directives than `max-age`, they are concatenated with the `max-age` directive that is added by the `ExpiresFilter`.

#### Expiration configuration selection

The expiration configuration if elected according to the following algorithm:

1. `ExpiresByType` matching the exact content-type returned by `HttpServletResponse.getContentType()` possibly including the charset (e.g. '`text/xml;charset=UTF-8`'),
2. `ExpiresByType` matching the content-type without the charset if `HttpServletResponse.getContentType()` contains a charset (e.g. '`text/xml;charset=UTF-8`' -> '`text/xml`'),
3. `ExpiresByType` matching the major type (e.g. substring before '`/`') of `HttpServletResponse.getContentType()` (e.g. '`text/xml;charset=UTF-8`' -> '`text`'),
4. `ExpiresDefault`

#### Filter Class Name

The filter class name for the Expires Filter is `org.apache.catalina.filters.ExpiresFilter` .

#### Initialisation parameters

The Expires Filter supports the following initialisation parameters:

Attribute | Description
--- | ---
`ExpiresExcludedResponseStatusCodes` | This directive defines the http response status codes for which the `ExpiresFilter` will not generate expiration headers. By default, the `304` status code ("`Not modified`") is skipped. The value is a comma separated list of http status codes. This directive is useful to ease usage of `ExpiresDefault` directive. Indeed, the behavior of `304 Not modified` (which does specify a `Content-Type` header) combined with `Expires` and `Cache-Control:max-age=` headers can be unnecessarily tricky to understand. See sample below the table
`ExpiresByType <content-type>` | This directive defines the value of the `Expires` header and the `max-age` directive of the `Cache-Control` header generated for documents of the specified type (e.g., `text/html`). The second argument sets the number of seconds that will be added to a base time to construct the expiration date. The `Cache-Control: max-age` is calculated by subtracting the request time from the expiration date and expressing the result in seconds. The base time is either the last modification time of the file, or the time of the client's access to the document. Which should be used is specified by the `<code>` field; `M` means that the file's last modification time should be used as the base time, and `A` means the client's access time should be used. The duration is expressed in seconds. `A2592000` stands for `access plus 30 days` in alternate syntax. The difference in effect is subtle. If `M` (`modification` in alternate syntax) is used, all current copies of the document in all caches will expire at the same time, which can be good for something like a weekly notice that's always found at the same URL. If `A` ( `access` or `now` in alternate syntax) is used, the date of expiration is different for each client; this can be good for image files that don't change very often, particularly for a set of related documents that all refer to the same images (i.e., the images will be accessed repeatedly within a relatively short timespan). Note: When the content type includes a charset (e.g. `'ExpiresByType text/xml;charset=utf-8'`), Tomcat removes blank chars between the '`;`' and the '`charset`' keyword. Due to this, configuration of an expiration with a charset must not include such a space character. See sample below the table It overrides, for the specified MIME type only, any expiration date set by the `ExpiresDefault` directive. You can also specify the expiration time calculation using an alternate syntax, described earlier in this document.
`ExpiresDefault` | This directive sets the default algorithm for calculating the expiration time for all documents in the affected realm. It can be overridden on a type-by-type basis by the `ExpiresByType` directive. See the description of that directive for details about the syntax of the argument, and the "alternate syntax" description as well.

Sample: exclude response status codes 302, 500 and 503

    <init-param>
     <param-name>ExpiresExcludedResponseStatusCodes</param-name>
     <param-value>302, 500, 503</param-value>
    </init-param>

Sample for ExpiresByType initialization parameter

    <init-param>
       <param-name>ExpiresByType text/html</param-name>
       <param-value>access plus 1 month 15   days 2 hours</param-value>
    </init-param>

    <init-param>
       <!-- 2592000 seconds = 30 days -->
       <param-name>ExpiresByType image/gif</param-name>
       <param-value>A2592000</param-value>
    </init-param>

#### Troubleshooting

To troubleshoot, enable logging on the `org.apache.catalina.filters.ExpiresFilter`.

Extract of logging.properties

    org.apache.catalina.filters.ExpiresFilter.level = FINE

Sample of initialization log message:

    Mar 26, 2010 2:01:41 PM org.apache.catalina.filters.ExpiresFilter init
    FINE: Filter initialized with configuration ExpiresFilter[
     excludedResponseStatusCode=[304],
     default=null,
     byType={
        image=ExpiresConfiguration[startingPoint=ACCESS_TIME, duration=[10 MINUTE]],
        text/css=ExpiresConfiguration[startingPoint=ACCESS_TIME, duration=[10 MINUTE]],
        text/javascript=ExpiresConfiguration[startingPoint=ACCESS_TIME, duration=[10 MINUTE]]}]

Sample of per-request log message where `ExpiresFilter` adds an expiration date is below. The message is on one line and is wrapped here for better readability.

    Mar 26, 2010 2:09:47 PM org.apache.catalina.filters.ExpiresFilter onBeforeWriteResponseBody
    FINE: Request "/tomcat.gif" with response status "200"
     content-type "image/gif", set expiration date 3/26/10 2:19 PM

Sample of per-request log message where `ExpiresFilter` does not add an expiration date:

    Mar 26, 2010 2:10:27 PM org.apache.catalina.filters.ExpiresFilter onBeforeWriteResponseBody
    FINE: Request "/docs/config/manager.html" with response status "200"
     content-type "text/html", no expiration configured

### 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.

### HTTP Header Security Filter

#### Introduction

There are a number of HTTP headers that can be added to the response to improve the security of the connection. This filter provides a mechanism for adding those headers. Note that security related headers with more complex requirements, like CORS, are implemented as separate Filters.

#### Filter Class Name

The filter class name for the HTTP Header Security Filter is `org.apache.catalina.filters.HttpHeaderSecurityFilter` .

#### Initialisation parameters

The HTTP Header Security Filter supports the following initialization parameters:

Attribute | Description
--- | ---
`hstsEnabled` | Will an HTTP Strict Transport Security (HSTS) header (`Strict-Transport-Security`) be set on the response for secure requests. Any HSTS header already present will be replaced. See RFC 6797 for further details of HSTS. If not specified, the default value of `true` will be used.
`hstsMaxAgeSeconds` | The max age value that should be used in the HSTS header. Negative values will be treated as zero. If not specified, the default value of `0` will be used.
`hstsIncludeSubDomains` | Should the includeSubDomains parameter be included in the HSTS header. If not specified, the default value of `false` will be used.
`hstsPreload` | Should the preload parameter be included in the HSTS header. If not specified, the default value of `false` will be used. See https://hstspreload.org for important information about this parameter.
`antiClickJackingEnabled` | Should the anti click-jacking header (`X-Frame-Options`) be set on the response. Any anti click-jacking header already present will be replaced. If not specified, the default value of `true` will be used.
`antiClickJackingOption` | What value should be used for the anticlick-jacking header? Must be one of `DENY`, `SAMEORIGIN`, `ALLOW-FROM` (case-insensitive). If not specified, the default value of `DENY` will be used.
`antiClickJackingUri` | If ALLOW-FROM is used for antiClickJackingOption, what URI should be allowed? If not specified, the default value of an empty string will be used.
`blockContentTypeSniffingEnabled` | Should the header that blocks content type sniffing (`X-Content-Type-Options`) be set on every response. If already present, the header will be replaced. If not specified, the default value of `true` will be used.
`xssProtectionEnabled` | Should the header that enables the browser's cross-site scripting filter protection (`X-XSS-Protection: 1; mode=block`) be set on every response. If already present, the header will be replaced. If not specified, the default value of `true` will be used.

### Remote Address Filter

#### Introduction

The Remote Address Filter allows you to compare the IP address of the client that submitted this request against one or more regular expressions, and either allow the request to continue or refuse to process the request from this client.

The syntax for regular expressions is different than that for 'standard' wildcard matching. Tomcat uses the `java.util.regex` package. Please consult the Java documentation for details of the expressions supported.

Note: There is a caveat when using this filter with IPv6 addresses. Format of the IP address that this valve is processing depends on the API that was used to obtain it. If the address was obtained from Java socket using Inet6Address class, its format will be `x:x:x:x:x:x:x:x`. That is, the IP address for localhost will be `0:0:0:0:0:0:0:1` instead of the more widely used `::1`. Consult your access logs for the actual value.

See also: Remote Host Filter.

#### Filter Class Name

The filter class name for the Remote Address Filter is `org.apache.catalina.filters.RemoteAddrFilter` .

#### Initialisation parameters

The Remote Address Filter supports the following initialisation parameters:

Attribute | Description
--- | ---
`allow` | A regular expression (using `java.util.regex`) that the remote client's IP address is compared to. If this attribute is specified, the remote address MUST match for this request to be accepted. If this attribute is not specified, all requests will be accepted UNLESS the remote address matches a `deny` pattern.
`deny` | A regular expression (using `java.util.regex`) that the remote client's IP address is compared to. If this attribute is specified, the remote address MUST NOT match for this request to be accepted. If this attribute is not specified, request acceptance is governed solely by the `accept` attribute.
`denyStatus` | HTTP response status code that is used when rejecting denied request. The default value is `403`. For example, it can be set to the value `404`.

#### Example

To allow access only for the clients connecting from localhost:

        <filter>
          <filter-name>Remote Address Filter</filter-name>
          <filter-class>org.apache.catalina.filters.RemoteAddrFilter</filter-class>
          <init-param>
            <param-name>allow</param-name>
            <param-value>127\.\d+\.\d+\.\d+|::1|0:0:0:0:0:0:0:1</param-value>
          </init-param>
        </filter>
        <filter-mapping>
          <filter-name>Remote Address Filter</filter-name>
          <url-pattern>/*</url-pattern>
        </filter-mapping>

### Remote Host Filter

#### Introduction

The Remote Host Filter allows you to compare the hostname of the client that submitted this request against one or more regular expressions, and either allow the request to continue or refuse to process the request from this client.

The syntax for regular expressions is different than that for 'standard' wildcard matching. Tomcat uses the `java.util.regex` package. Please consult the Java documentation for details of the expressions supported.

Note: This filter processes the value returned by method `ServletRequest.getRemoteHost()`. To allow the method to return proper host names, you have to enable "DNS lookups" feature on a Connector.

See also: Remote Address Filter, HTTP Connector configuration.

#### Filter Class Name

The filter class name for the Remote Address Filter is `org.apache.catalina.filters.RemoteHostFilter` .

#### Initialisation parameters

The Remote Host Filter supports the following initialisation parameters:

Attribute | Description
--- | ---
`allow` | A regular expression (using `java.util.regex`) that the remote client's hostname is compared to. If this attribute is specified, the remote hostname MUST match for this request to be accepted. If this attribute is not specified, all requests will be accepted UNLESS the remote hostname matches a `deny` pattern.
`deny` | A regular expression (using `java.util.regex`) that the remote client's hostname is compared to. If this attribute is specified, the remote hostname MUST NOT match for this request to be accepted. If this attribute is not specified, request acceptance is governed solely by the `accept` attribute.
`denyStatus` | HTTP response status code that is used when rejecting denied request. The default value is `403`. For example, it can be set to the value `404`.

### Remote CIDR Filter

#### Introduction

The Remote CIDR Filter allows you to compare the IP address of the client that submitted this request against one or more netmasks following the CIDR notation, and either allow the request to continue or refuse to process the request from this client. IPv4 and IPv6 are both fully supported.

This filter mimicks Apache httpd's `Order`, `Allow from` and `Deny from` directives, with the following limitations:

- `Order` will always be `allow, deny`;
- dotted quad notations for netmasks are not supported (that is, you cannot write `192.168.1.0/255.255.255.0`, you must write `192.168.1.0/24`;
- shortcuts, like `10.10.`, which is equivalent to `10.10.0.0/16`, are not supported;
- as the filter name says, this is a CIDR only filter, therefore subdomain notations like `.mydomain.com` are not supported either.

Some more features of this filter are:

- if you omit the CIDR prefix, this filter becomes a single IP filter;
- unlike the Remote Host Filter, it can handle IPv6 addresses in condensed form (`::1`, `fe80::/71`, etc).

#### Filter Class Name

The filter class name for the Remote Address Filter is `org.apache.catalina.filters.RemoteCIDRFilter` .

#### Initialisation parameters

The Remote CIDR Filter supports the following initialisation parameters:

Attribute | Description
--- | ---
`allow` | A comma-separated list of IPv4 or IPv6 netmasks or addresses that the remote client's IP address is matched against. If this attribute is specified, the remote address MUST match for this request to be accepted. If this attribute is not specified, all requests will be accepted UNLESS the remote IP is matched by a netmask in the `deny` attribute.
`deny` | A comma-separated list of IPv4 or IPv6 netmasks or addresses that the remote client's IP address is matched against. If this attribute is specified, the remote address MUST NOT match for this request to be accepted. If this attribute is not specified, request acceptance is governed solely by the `accept` attribute.

#### Example

To allow access only for the clients connecting from localhost:

          <filter>
          <filter-name>Remote CIDR Filter</filter-name>
          <filter-class>org.apache.catalina.filters.RemoteCIDRFilter</filter-class>
          <init-param>
          <param-name>allow</param-name>
          <param-value>127.0.0.0/8, ::1</param-value>
          </init-param>
          </filter>
          <filter-mapping>
          <filter-name>Remote CIDR Filter</filter-name>
          <url-pattern>/*</url-pattern>
          </filter-mapping>

### Remote IP Filter

#### Introduction

Tomcat port of mod_remoteip, this filter replaces the apparent client remote IP address and hostname for the request with the IP address list presented by a proxy or a load balancer via a request headers (e.g. "X-Forwarded-For").

Another feature of this filter is to replace the apparent scheme (http/https), server port and `request.secure` with the scheme presented by a proxy or a load balancer via a request header (e.g. "X-Forwarded-Proto").

If used in conjunction with Remote Address/Host filters then this filter should be defined first to ensure that the correct client IP address is presented to the Remote Address/Host filters.

Note: By default this filter has no effect on the values that are written into access log. The original values are restored when request processing leaves the filter and that always happens earlier than access logging. To pass the remote address, remote host, server port and protocol values set by this filter to the access log, they are put into request attributes. Publishing these values here is enabled by default, but `AccessLogValve` should be explicitly configured to use them. See documentation for `requestAttributesEnabled` attribute of `AccessLogValve`.

The names of request attributes that are set by this filter and can be used by access logging are the following:

- `org.apache.catalina.AccessLog.RemoteAddr`
- `org.apache.catalina.AccessLog.RemoteHost`
- `org.apache.catalina.AccessLog.Protocol`
- `org.apache.catalina.AccessLog.ServerPort`
- `org.apache.tomcat.remoteAddr`

#### Filter Class Name

The filter class name for the Remote IP Filter is `org.apache.catalina.filters.RemoteIpFilter` .

#### Basic configuration to handle 'x-forwarded-for'

The filter will process the `x-forwarded-for` http header.

          <filter>
            <filter-name>RemoteIpFilter</filter-name>
            <filter-class>org.apache.catalina.filters.RemoteIpFilter</filter-class>
          </filter>

          <filter-mapping>
            <filter-name>RemoteIpFilter</filter-name>
            <url-pattern>/*</url-pattern>
            <dispatcher>REQUEST</dispatcher>
          </filter-mapping>

#### Basic configuration to handle 'x-forwarded-for' and 'x-forwarded-proto'

The filter will process `x-forwarded-for` and `x-forwarded-proto` http headers. Expected value for the `x-forwarded-proto` header in case of SSL connections is `https` (case insensitive).

          <filter>
            <filter-name>RemoteIpFilter</filter-name>
            <filter-class>org.apache.catalina.filters.RemoteIpFilter</filter-class>
            <init-param>
              <param-name>protocolHeader</param-name>
              <param-value>x-forwarded-proto</param-value>
            </init-param>
          </filter>

          <filter-mapping>
            <filter-name>RemoteIpFilter</filter-name>
            <url-pattern>/*</url-pattern>
            <dispatcher>REQUEST</dispatcher>
          </filter-mapping>

#### Advanced configuration with internal proxies

RemoteIpFilter configuration:

         <filter>
           <filter-name>RemoteIpFilter</filter-name>
           <filter-class>org.apache.catalina.filters.RemoteIpFilter</filter-class>
           <init-param>
             <param-name>allowedInternalProxies</param-name>
             <param-value>192\.168\.0\.10|192\.168\.0\.11</param-value>
           </init-param>
           <init-param>
             <param-name>remoteIpHeader</param-name>
             <param-value>x-forwarded-for</param-value>
           </init-param>
           <init-param>
             <param-name>remoteIpProxiesHeader</param-name>
             <param-value>x-forwarded-by</param-value>
           </init-param>
           <init-param>
             <param-name>protocolHeader</param-name>
             <param-value>x-forwarded-proto</param-value>
           </init-param>
         </filter>

Request values:

Property | Value Before RemoteIpFilter | Value After RemoteIpFilter
--- | --- | ---
request.remoteAddr | 192.168.0.10 | 140.211.11.130
request.header`[`'x-forwarded-for'`]` | 140.211.11.130, 192.168.0.10 | null
request.header`[`'x-forwarded-by'`]` | null | null
request.header`[`'x-forwarded-proto'`]` | https | https
request.scheme | http | https
request.secure | false | true
request.serverPort | 80 | 443

Note : `x-forwarded-by` header is `null` because only internal proxies has been traversed by the request. `x-forwarded-for` is `null` because all the proxies are trusted or internal.

#### Advanced configuration with trusted proxies

RemoteIpFilter configuration:

         <filter>
           <filter-name>RemoteIpFilter</filter-name>
           <filter-class>org.apache.catalina.filters.RemoteIpFilter</filter-class>
           <init-param>
             <param-name>allowedInternalProxies</param-name>
             <param-value>192\.168\.0\.10|192\.168\.0\.11</param-value>
           </init-param>
           <init-param>
             <param-name>remoteIpHeader</param-name>
             <param-value>x-forwarded-for</param-value>
           </init-param>
           <init-param>
             <param-name>remoteIpProxiesHeader</param-name>
             <param-value>x-forwarded-by</param-value>
           </init-param>
           <init-param>
             <param-name>trustedProxies</param-name>
             <param-value>proxy1|proxy2</param-value>
           </init-param>
         </filter>

Request values:

Property | Value Before RemoteIpFilter | Value After RemoteIpFilter
--- | --- | ---
request.remoteAddr | 192.168.0.10 | 140.211.11.130
request.header`[`'x-forwarded-for'`]` | 140.211.11.130, proxy1, proxy2 | null
request.header`[`'x-forwarded-by'`]` | null | proxy1, proxy2

Note : `proxy1` and `proxy2` are both trusted proxies that come in `x-forwarded-for` header, they both are migrated in `x-forwarded-by` header. `x-forwarded-for` is `null` because all the proxies are trusted or internal.

#### Advanced configuration with internal and trusted proxies

RemoteIpFilter configuration:

         <filter>
           <filter-name>RemoteIpFilter</filter-name>
           <filter-class>org.apache.catalina.filters.RemoteIpFilter</filter-class>
           <init-param>
             <param-name>allowedInternalProxies</param-name>
             <param-value>192\.168\.0\.10|192\.168\.0\.11</param-value>
           </init-param>
           <init-param>
             <param-name>remoteIpHeader</param-name>
             <param-value>x-forwarded-for</param-value>
           </init-param>
           <init-param>
             <param-name>remoteIpProxiesHeader</param-name>
             <param-value>x-forwarded-by</param-value>
           </init-param>
           <init-param>
             <param-name>trustedProxies</param-name>
             <param-value>proxy1|proxy2</param-value>
           </init-param>
         </filter>

Request values:

Property | Value Before RemoteIpFilter | Value After RemoteIpFilter
--- | --- | ---
request.remoteAddr | 192.168.0.10 | 140.211.11.130
request.header`[`'x-forwarded-for'`]` | 140.211.11.130, proxy1, proxy2, 192.168.0.10 | null
request.header`[`'x-forwarded-by'`]` | null | proxy1, proxy2

Note : `proxy1` and `proxy2` are both trusted proxies that come in `x-forwarded-for` header, they both are migrated in `x-forwarded-by` header. As `192.168.0.10` is an internal proxy, it does not appear in `x-forwarded-by`. `x-forwarded-for` is `null` because all the proxies are trusted or internal.

#### Advanced configuration with an untrusted proxy

RemoteIpFilter configuration:

         <filter>
           <filter-name>RemoteIpFilter</filter-name>
           <filter-class>org.apache.catalina.filters.RemoteIpFilter</filter-class>
           <init-param>
             <param-name>allowedInternalProxies</param-name>
             <param-value>192\.168\.0\.10|192\.168\.0\.11</param-value>
           </init-param>
           <init-param>
             <param-name>remoteIpHeader</param-name>
             <param-value>x-forwarded-for</param-value>
           </init-param>
           <init-param>
             <param-name>remoteIpProxiesHeader</param-name>
             <param-value>x-forwarded-by</param-value>
           </init-param>
           <init-param>
             <param-name>trustedProxies</param-name>
             <param-value>proxy1|proxy2</param-value>
           </init-param>
         </filter>

Request values:

Property | Value Before RemoteIpFilter | Value After RemoteIpFilter
--- | --- | ---
request.remoteAddr | 192.168.0.10 | untrusted-proxy
request.header`[`'x-forwarded-for'`]` | 140.211.11.130, untrusted-proxy, proxy1 | 140.211.11.130
request.header`[`'x-forwarded-by'`]` | null | proxy1

Note : `x-forwarded-by` holds the trusted proxy `proxy1`. `x-forwarded-by` holds `140.211.11.130` because `untrusted-proxy` is not trusted and thus, we cannot trust that `untrusted-proxy` is the actual remote ip. `request.remoteAddr` is `untrusted-proxy` that is an IP verified by `proxy1`.

#### Initialisation parameters

The Remote IP Filter supports the following initialisation parameters:

Attribute | Description
--- | ---
`remoteIpHeader` | Name of the HTTP Header read by this valve that holds the list of traversed IP addresses starting from the requesting client. If not specified, the default of `x-forwarded-for` is used.
`internalProxies` | Regular expression (using `java.util.regex`) that a proxy's IP address must match to be considered an internal proxy. Internal proxies that appear in the remoteIpHeader will be trusted and will not appear in the proxiesHeader value. If not specified the default value of `10\.\d{1,3}\.\d{1,3}\.\d{1,3}|192\.168\.\d{1,3}\.\d{1,3}|169\.254\.\d{1,3}\.\d{1,3}|127\.\d{1,3}\.\d{1,3}\.\d{1,3}|172\.1[6-9]{1}\.\d{1,3}\.\d{1,3}|172\.2[0-9]{1}\.\d{1,3}\.\d{1,3}|172\.3[0-1]{1}\.\d{1,3}\.\d{1,3}|0:0:0:0:0:0:0:1` will be used.
`proxiesHeader` | Name of the HTTP header created by this valve to hold the list of proxies that have been processed in the incoming remoteIpHeader. If not specified, the default of `x-forwarded-by` is used.
`requestAttributesEnabled` | Set to `true` to set the request attributes used by AccessLog implementations to override the values returned by the request for remote address, remote host, server port and protocol. Request attributes are also used to enable the forwarded remote address to be displayed on the status page of the Manager web application. If not set, the default value of `true` will be used.
`trustedProxies` | Regular expression (using `java.util.regex`) that a proxy's IP address must match to be considered an trusted proxy. Trusted proxies that appear in the remoteIpHeader will be trusted and will appear in the proxiesHeader value. If not specified, no proxies will be trusted.
`protocolHeader` | Name of the HTTP Header read by this valve that holds the protocol used by the client to connect to the proxy. If not specified, the default of `X-Forwarded-Proto` is used.
`hostHeader` | Name of the HTTP Header read by this valve that holds the host used by the client to connect to the proxy. If not specified, the default of `null` is used.
`portHeader` | Name of the HTTP Header read by this valve that holds the port used by the client to connect to the proxy. If not specified, the default of `null` is used.
`protocolHeaderHttpsValue` | Value of the protocolHeader to indicate that it is an HTTPS request. If not specified, the default of `https` is used.
`httpServerPort` | Value returned by `ServletRequest.getServerPort()` when the protocolHeader indicates `http` protocol and no portHeader is present. If not specified, the default of `80` is used.
`httpsServerPort` | Value returned by `ServletRequest.getServerPort()` when the protocolHeader indicates `https` protocol and no portHeader is present. If not specified, the default of `443` is used.
`changeLocalName` | If `true`, the value returned by `ServletRequest.getLocalName()` and `ServletRequest.getServerName()` is modified by the this filter. If not specified, the default of `false` is used.
`changeLocalPort` | If `true`, the value returned by `ServletRequest.getLocalPort()` and `ServletRequest.getServerPort()` is modified by the this filter. If not specified, the default of `false` is used.

### Request Dumper Filter

#### Introduction

The Request Dumper Filter logs information from the request and response objects and is intended to be used for debugging purposes. When using this Filter, it is recommended that the `org.apache.catalina.filter.RequestDumperFilter` logger is directed to a dedicated file and that the `org.apache.juli.VerbatimFormatter` is used.

WARNING: Using this filter has side-effects. The output from this filter includes any parameters included with the request. The parameters will be decoded using the default platform encoding. Any subsequent calls to `request.setCharacterEncoding()` within the web application will have no effect.

#### Filter Class Name

The filter class name for the Request Dumper Filter is `org.apache.catalina.filters.RequestDumperFilter` .

#### Initialisation parameters

The Request Dumper Filter does not support any initialization parameters.

#### Sample Configuration

The following entries in a web application's web.xml would enable the Request Dumper filter for all requests for that web application. If the entries were added to `CATALINA_BASE/conf/web.xml`, the Request Dumper Filter would be enabled for all web applications.

    <filter>
        <filter-name>requestdumper</filter-name>
        <filter-class>
            org.apache.catalina.filters.RequestDumperFilter
        </filter-class>
    </filter>
    <filter-mapping>
        <filter-name>requestdumper</filter-name>
        <url-pattern>*</url-pattern>
    </filter-mapping>

The following entries in CATALINA_BASE/conf/logging.properties would create a separate log file for the Request Dumper Filter output.

    # To this configuration below, 1request-dumper.org.apache.juli.FileHandler
    # also needs to be added to the handlers property near the top of the file
    1request-dumper.org.apache.juli.FileHandler.level = INFO
    1request-dumper.org.apache.juli.FileHandler.directory = ${catalina.base}/logs
    1request-dumper.org.apache.juli.FileHandler.prefix = request-dumper.
    1request-dumper.org.apache.juli.FileHandler.encoding = UTF-8
    1request-dumper.org.apache.juli.FileHandler.formatter = org.apache.juli.VerbatimFormatter
    org.apache.catalina.filters.RequestDumperFilter.level = INFO
    org.apache.catalina.filters.RequestDumperFilter.handlers = \
      1request-dumper.org.apache.juli.FileHandler

### Session Initializer Filter

#### Introduction

The Session Initializer Filter initializes the `javax.servlet.http.HttpSession` before the Request is processed. This is required for JSR-356 compliant WebSocket implementations, if the `HttpSession` is needed during the HandShake phase.

The Java API for WebSocket does not mandate that an `HttpSession` would be initialized upon request, and thus `javax.servlet.http.HttpServletRequest`'s `getSession()` returns `null` if the `HttpSession` was not initialized in advance.

This filter solves that problem by initializing the HttpSession for any `HttpServletRequest` that matches its `url-pattern`.

#### Filter Class Name

The filter class name for the Session Initializer Filter is `org.apache.catalina.filters.SessionInitializerFilter`.

#### Initialisation parameters

The Session Initializer Filter does not support any initialization parameters.

#### Sample Configuration

The following entries in the Web Application Deployment Descriptor, web.xml, would enable the Session Initializer Filter for requests that match the given URL pattern (in this example, "/ws/*").

    <filter>
        <filter-name>SessionInitializer</filter-name>
        <filter-class>org.apache.catalina.filters.SessionInitializerFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>SessionInitializer</filter-name>
        <url-pattern>/ws/*</url-pattern>
    </filter-mapping>

### 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`.

### WebDAV Fix Filter

#### Introduction

Microsoft operating systems have two WebDAV clients. One is used with port 80, the other is used for all other ports. The implementation used with port 80 does not adhere to the WebDAV specification and fails when trying to communicate with the Tomcat WebDAV Servlet. This Filter provides a fix for this by forcing the use of the WebDAV implementation that works, even when connecting via port 80.

#### Filter Class Name

The filter class name for the WebDAV Fix Filter is `org.apache.catalina.filters.WebdavFixFilter` .

#### Initialisation parameters

The WebDAV Fix Filter does not support any initialization parameters.