Filters

Java filters were introduced in the Java Servlet specification version 2.3. A filter intercepts requests and responses to transform or use the information. Filters typically do not themselves create responses but instead provide universal functions that can be attached to any type of servlet page.

Since the filter chain is responsible for request handling in Magnolia, the default chain illustrates how filters are used to process requests. This document provides minimal information on filters. For more, see Request processing and filters and the filters package.

Don’t change the filter order

Magnolia handles incoming requests to display a page through its own filter chain. Filters in the chain are executed in the order in which they are declared until a filter decides that it can fulfill the request.

Be careful

When editing properties in the filter chain be careful. Always test the changes on test environment before applying it to production.

For instance, if you add a Voter to a filter with an erroneous regular expression, you won’t be able to access the Admincentral anymore. In such case you have to use Groovy Rescue App.

Context

The first filter in the filter chain is ContextFilter. This filter initializes MgnlContext and configures MDC logging. MgnlContext is local to the request and available on every further filter. The context provides a lot of useful functions, see MgnlContext for details.

Content type

The job of the ContentTypeFilter is to initialize AggregationState.

It’s created and populated with:

  • Character encoding

  • Original URI

  • Original URL

  • Extension

  • Query string

The AggregationState is accessible using MgnlContext.getAggregationState().

The Content-Type header is not set by ContentTypeFilter anymore. The MIME type was incorrectly set according to the request extension. It is now the responsibility of renderers/servlets to set the correct content type. For instance, FreemarkerRenderer sets the content type.

Content type filter can be configured to match requests to content types. See Restricting responses to configured MIME types.

Cookies detector

CookiesDetectorFilter is a personalization filter that detects request cookies and adds them as traits to the aggregation state.

Date

DateDetectorFilter is a simple date trait filter for personalization that stores the current system time in the TraitCollector.

Country

CountryDetectorFilter is a GeoIP trait filter that detects the user’s country using the IP address of the request for personalization. It adds the country to the aggregation state as a trait. If a GET parameter Country#REQUEST_PARAMETER with an IP address is supplied, this address is used to resolve the country, which is stored in the TraitCollector.

Visitor

VisitorDetectorFilter is a visitor traitfilter that detects the type of visitor based on the current user and cookies for personalization.

visitorCookies can be configured for returning and registered users.

/server/filters/visitor/
class: info.magnolia.personalization.visitor.VisitorDetectorFilter
returning:
  level: 5
  name: VISITOR
  value: returning
registered:
  name: VISITOR
  value: registered
new:
  maxAge: 86400
  name: NEW_VISITOR
  value: new

Additional Properties

(Applicable to the cookie name nodes, i.e. to returning, registered and new in the above examples.)

Property Description

httpOnlyCookie

optional, default is false

A security setting that prevents cookies from being read by potentially malicious code.

secureCookie

optional, default is false

Setting the property to true (recommended) will prevent cookies from being sent if the protocol used is insecure (HTTP instead of HTTPS).

Multipart request

MultipartRequestFilter is a filter that determines if a HttpServletRequest contains multipart content, and if so parses it into a request attribute for further processing.

The maximum number of files allowed per request can be configured using the fileCountMax parameter. The parameter defaults to 10. However, fileCountMax does not apply to publication requests because they are authenticated internally. The maximum file size in bytes can be configured using the maxFileSize parameter. The parameter defaults to 2000000000 (two gigabytes).

/server/filters/multipartRequest/
class: info.magnolia.cms.security.MultipartRequestFilter
fileCountMax: 10
maxFileSize: 2000000000

Unicode Normalization

UnicodeNormalizationFilter normalizes the current URI to the NFC form that is used internally.

Registration

RegistrationFilter checks the validity of the registration of a DX Core installation and delegates to the registration form so that the user can enter the license key. The license is also checked in other parts of the code such as in the STK.

Login

Handles incoming login requests and delegates to login handlers. The handlers are configured under this filter.

info.magnolia.cms.security.auth.login.LoginFilter verifies that user credentials have been authenticated so that only authenticated users can be made active users. Magnolia uses JAAS for authentication. For more information, see Security.

Redirecting via the mgnlReturnTo request parameter after login is only permitted for relative URLs or for URLs explicitly added to the info.magnolia.cms.security.auth.login.LoginFilter configuration.

To whitelist URLs, add the UrlPattern instances of all allowed redirects to server/filter/login/allowedRedirects.

GZip

To improve site performance, GZipFilter replaces text type responses with the gzipped response. The trick in this filter is that it passes a ResponseWrapper instead of the response object it got in the doFilter(..) call to the filter chain. After all the following filters have been executed, content is extracted from the ResponseWrapper, gzipped and written to the original response.

Channel

MultiChannelFilter resolves the channel to use by considering variations of the set channel. Resulting site gets set in ExtendedAggregationState.

Multisite

MultiSiteFilter is a DX Core filter. It detects which site definition should be used. The filter makes site related properties available in AggregationState.

Site merge

SiteMergeFilter merges channel variations with the site definition. Configurations under this filter override configuration done in the site definition. The filter sets the site definition in the aggregation state. In the Community Edition, this filter sets the site in the aggregation state. In DX Core, the multisite filter can also set the site.

Logout

LogoutFilter checks to see if the logout attribute mgnlLogout is set as a request parameter. If this flag is found, the user will be logged out and the filter chain will restart with the first filter.

Security callback

SecurityCallbackFilter handles 401 and 403 HTTP response codes and AccessDeniedExceptions. The filter renders an appropriate login form that can consist of a redirect or anything else.

Multiple HttpClientCallbacks with different configuration and behavior can be configured for this filter.

Here is the client callback configuration for the Travel Demo members area redirect and login form.

/server/filters/securityCallback/
class: info.magnolia.cms.security.SecurityCallbackFilter
clientCallbacks:
  travel-demo-pur:
    class: info.magnolia.cms.security.auth.callback.RedirectClientCallback
    location: /travel/members/login.html
    originalUrlPattern:
      class: info.magnolia.cms.util.SimpleUrlPattern
      patternString: (*|travel)/members/(profile-update|protected)*
  form:
    class: info.magnolia.cms.security.auth.callback.FormClientCallback
    loginForm: /defaultMagnoliaLoginForm/login.html
Both callback classes implement the HttpClientCallback interface and support their own configuration properties. A custom callback should implement this interface.

Classes:

  • RedirectClientCallback redirects to a configured path or URL. This is useful, for example, in single sign-on (SSO) context where the login screen is handled by a different application, or to hide the login form from a public instance using a fronting server configuration.

  • FormClientCallback renders a login form using FreeMarker and the template configured with loginForm.

AbstractHttpClientCallback provides a number of filtering capabilities:

  • url. Current request URL decoded and without the context path.

  • urlPattern

  • originalUrl. Original request URL decoded and without the context path, but not modified by any filter.

  • originalUrlPattern

  • hostPattern

  • voters

For example, in a multisite installation for the request http://demo.magnolia-cms.com/travel/about.html:

  • url is /about.html

  • originalUrl is /travel/about.html

The Multisite filter removes the first-level node name from the URL.

The methods provided by AbstractHttpClientCallback are also provided by the UrlPatternDelegate utility class.

CSRF security

CsrfSecurityFilter

CsrfSecurityFilter checks the HTTP referer header to ensure that the request is not a cross-site request forgery attack. When a possible CSRF attack is detected, the browser returns a 400 Bad Request error and Magnolia logs a security warning to the audit log.

CsrfSecurityFilter causes a request to fail if:

  • The referer header is empty.

    Host: mysite.com/.magnolia/pages/adminCentral.html
Referer:

  • The host part of the referer header does not match the requested host.

    Host: mysite.com/.magnolia/pages/adminCentral.html
Referer: hackersite.io

If you access Magnolia with a script, set the referer header in your script to ensure the script can access Magnolia. Similarly, if you embed Magnolia content into a different website, disable CsrfSecurityFilter or add a voter that bypasses the CSRF filter for any requests coming from the trusted URL.

Bypassing CsrfSecurityFilter

You can bypass the CSRF security filter via a voter. By default, CsrfSecurityFilter is bypassed if:

  • The requested URL does not start with /.magnolia. Only Admincentral URLs are vulnerable to CSRF attacks; other URLs are not checked.

  • The user is not authenticated for Admincentral access. Only authenticated requests are vulnerable to CSRF attacks.

  • The request does not have query parameters.

  • The requested resource is somewhere in Admincentral. Vaadin has its own CSRF protection, so Magnolia hands the responsibility over to Vaadin.

You can create your own whitelist of referer domains or URIs using a voter. The filter is bypassed for the whitelisted referers. In the following example, the filter is bypassed for any requests referred by http://www.example.com.

/server/filters/csrfSecurity/
class: info.magnolia.cms.security.CsrfSecurityFilter
bypasses:
  whitelist:
    class: info.magnolia.voting.voters.RequestHeaderPatternSimpleVoter
    headerName: referer
    pattern: http://wwww.example.com
Property Description

<voter node>

required

Voter node. Name the node, for example, whitelist.

     class

required

Fully qualified voter class name. Available classes:

  • info.magnolia.voting.voters.RequestHeaderPatternSimpleVoter checks for a URL pattern that complies with info.magnolia.cms.util.SimpleUrlPattern (for example, http://www.example.*).

  • info.magnolia.voting.voters.RequestHeaderPatternRegexVoter checks for a regular expression pattern.

     headerName

required

Header you want to check (for example, referer).

This is not a misspelling.

     pattern

required

Domain or URL pattern that complies with info.magnolia.cms.util.SimpleUrlPattern. The pattern must be present in the header for the filter to be bypassed.

CsrfSecurityFilter and Internet Explorer

Some builds of Internet Explorer do not send the HTTP referer header when submitting a form or when opening a popup. If the referer is not in the HTTP header, CsrfSecurityFilter#handlePossibleCsrf interprets the request as a potential CSRF attack, which forces the user to log in on the popup. To overcome this issue, add info.magnolia.voting.voters.UserAgentVoter as a voter class to bypass CsrfSecurityFilter for Internet Explorer.

/server/filters/csrfSecurity/
bypasses:
  userAgent:
    class: info.magnolia.voting.voters.UserAgentVoter
    allowed:
      IE11: .*Trident/7.0; rv:11.0.*

Under the allowed node, you can add a list of regular expressions to match the userAgent HTTP header. In the example above, Internet Explorer 11 is bypassed.

To ensure the filter is bypassed, make sure to have at least one property under the allowed node with a value that matches the userAgent of the browser for which you want to bypass the filter. For Internet Explorer 11, userAgent might be Mozilla/5.0 (Windows NT 6.3; Trident/7.0; rv:11.0) like Gecko.

Always test changes on a test environment before applying them to a production system. If you add an erroneous regular expression, you will not be able to access Admincentral anymore. In that case, you will have to use the Groovy Rescue App.

CsrfCookieTokenFilter and CsrfSessionTokenFilter

With Magnolia 6.2.14, CsrfCookieTokenFilter and CsrfSessionTokenFilter replaced the deprecated CsrfTokenSecurityFilter. These two classes cover the following functionality below.

Splitting the functionality across two classes simplifies implementation, allowing bypasses to be configured more specifically. Both filters define a CSRF token strategy that exposes methods for creating, validating and renewing tokens. The default strategy is HmacCsrfToken.
Magnolia 6.2.23+

From Magnolia 6.2.23, you can also set the secure and httpOnly attributes on the CSRF cookie. Set these through admincentral at /server/filters/csrfTokenSecurity/csrfLogin.

Attribute definitions

Property Description

httpOnlyCookie

optional, default is false

A security setting that prevents cookies from being read by potentially malicious code.

secureCookie

optional, default is false

Setting the property to true (recommended) will prevent cookies from being sent if the protocol used is insecure (HTTP instead of HTTPS).

Bypassing CsrfCookieTokenFilter and CsrfSessionTokenFilter

You can bypass the CSRF security filter via a voter. By default, both CsrfCookieTokenFilter and CsrfSessionTokenFilter are bypassed if:

  • In REST, the URL starts with /.rest.

  • In Activation, the URL starts with /.magnolia/activation.

  • In Vaadin heartbeat, the URL starts with /.magnolia/admincentral/HEARTBEAT.

  • In Vaadin, the URL starts with /.magnolia/admincentral/UIDL.

  • In Vaadin on Magnolia 5 Admincentral, the URL starts with /.magnolia/admincentral-m5/UIDL.

  • In DAM, the URL starts with /.dam.

  • In Imaging, the URL starts with /.imaging.

  • In Resources, the URL starts with /.resources.

  • In GraphQL, the URL starts with /.graphql.

In addition, CsrfSessionTokenFilter is bypassed by default if:

  • In Admincentral, the URL starts with /.magnolia/admincentral.

Cross-site security

CrossSiteSecurityFilter grants or denies permission to a site when the site is requested through a particular domain name. For example, if you only grant access to the travel site through www.mgnltravel.com, no other URL can be used to access the content. When a user tries to access one site’s content through another site’s domain name, the system displays a HTTP 404 error (page not found). See Cross-site security

URI security

URISecurityFilter checks to see if the active user has permission to access the requested URI. In DX Core, SiteUriSecurityFilter of Multisite module extends UriSecurityFilter to provide site-aware functionality.

The following constraints are considered in finding the permissions of the user:

  • URI ACLs of the user’s roles

  • URI ACLs of the user’s groups’ roles

  • Permissions on IP addresses

If the user does not have the permission to access the URI then JAAS will provide a login form. This default behavior of the URI security filter can be changed in JAAS configuration.

You can configure your own login form in the URI security filter to replace the default Magnolia login form. The form is configured in /server/filters/securityCallback/clientCallbacks. Here is an example of a custom form used to grant public users access to a restricted members area. Authentication is delegated to the custom form when a particular URI is accessed.

If you do not grant permission to the custom login form path, a standard Magnolia login form is displayed, usually on the author instance.

Range

RangeSupportFilter adds support for ranged requests. Ranged requests is used by iPhone and some other clients to stream videos. In contrast to Android phones, iPhone does not support any other method of streaming videos.

i18n content support

I18nContentSupportFilter detects the requested locale and sets the locale in the aggregation state. The filter rewrites the internal current URI, whether virtual or not. It does not rewrite the URI displayed to the user, however. See Language.

Cache

CacheFilter manages the Magnolia cache.

The cache filter checks if a requested resource is already stored in the cache to avoid recreation of the resource. If the resource is in the cache, then it will be written to the response and the filter chain stops. If the resource is not found in the cache, then a ResponseWrapper, which not only writes to the standard response but also saves the response, is passed to the chain. After the filters that follow have been executed (and the requested resource created), the content is extracted from the response wrapper and stored in the cache.

The cache filter is part of Cache core and the respective configuration can be found in the module configuration.

CORS

SelfConfiguredCorsFilter and SiteAwareCorsFilter (Magnolia 6.2.4+) handle simple and pre-flight requests for cross-origin resource sharing (CORS). For more details, see the CORS page.

Virtual URI

VirtualUriFilter checks if the requested URI matches a configured URI pattern and executes the URI mapping.

Servlets filter chain

The servlets configured in modules are installed in Magnolia’s servlets filter chain using ServletDispatchingFilter as the implementing filter class. If the servlet mapping matches the URI, then the service(..) method of the servlet is called. See Registering a servlet for more.

CMS filter chain

Finally, we arrive at the filter chain which does the page rendering and delivery. The filters are grouped in this filter chain so they share a co-bypass definition.

Repository mapping

RepositoryMappingFilter handles access to different workspaces. By default, Magnolia is connected with the website workspace. Therefore a request URI is interpreted as the path to a node in the website workspace. If you want to address nodes in other workspaces you need to specify a repository mapping in /server/URI2RepositoryMapping.

Content security

While the URI security filter checks permissions on the URI, ContentSecurityFilter checks if the current user has permission to access the requested content resource. The following constraints are considered in finding the permissions of the user:

  • Workspace-specific ACLs of the user’s roles

  • Workspace-specific ACLs of the user group’s roles

If the user does not have permission to the resource, then JAAS will provide a login form. This default behavior of the content security filter can be changed in JAAS configuration.

Aggregator

AggregatorFilter analyzes the request and stores the results in AggregationState. After this filter, every value the aggregation state can have is known.

Target

Collected information

Page

  • Content node of the requested page

  • Template

NodeData

  • NodeData object of the requested data

  • Template if a template is connected with the NodeData

Variant resolver

VariantResolverFilter is a personalization filter that wraps variant nodes. The filter tries to resolve a variant from the current node (from AggregationState) using all available traits stored in the TraitCollector and wraps it accordingly, if required. It only uses PersonalizationNodeWrapper if a variant was resolved. Non-variants are not wrapped.

/server/filters/cms/variantResolver/
wrapOnlyPersonalizedNodes: true
Property Description

wrapOnlyPersonalizedNodes

optional, default is false

If set to true, only page variants are wrapped.

Model execution

ModelExecutionFilter executes the component model before template rendering. The filter looks for a request parameter containing the UUID of the component to execute. The model can send output in which case page rendering is skipped, or return a URI prefixed by redirect, permanent or forward.

Rendering

Finally, RenderingFilter is responsible for delivering the requested resource. If the requested resource is data, such as a file, then the data is just copied to the response.

The rendering filter is terminal, meaning it ends the filter chain and filtering process. If no filter before it has been able to fulfill the request and the rendering filter cannot find the page either, then a 404 page not found error is returned. This is the default behavior.

You can change the behavior by adding a terminateChain property under the rendering filter and setting it to false. When a request for a page such as /home/some/page is received and no such page exists in the JCR, your own servlets can have a go at fulfilling the request. The default value for the terminateChain property is true.

Restricting access to resources

Access to resources is defined in the /modules/resources/config/resourceFilter filter. By default, the filter allows access to resources as follows:

  • byType

    • css, map, js, htm(l), ico, woff(2), ttf, svg, gif, jp(e)g, tiff, bmp

  • byLocation

    • when located in the webresources directory.

Adding HTTP headers

The AddHeadersFilter implementation class allows configuration of a filter for adding HTTP headers to enable, for example, Cross-origin resource sharing (CORS). The parameters configured in this filter are added to the HTTP header if the filter is triggered. You can restrict the filter’s scope by adding and configuring a bypasses node to it. For details please refer to the Magnolia main filter page.

Example configuration for CORS

Since Magnolia 6.2.4, you can use the cors filter to handle CORS requests.

The example allows CORS with header types X-Requested-With, Content-Type, Accept, with the GET method, and from any origin:

/server/filters/HeaderFilterOne/
class: info.magnolia.cms.filters.AddHeadersFilter
enabled: true
headers:
  Access-Control-Allow-Headers: X-Requested-With, Content-Type, Accept
  Access-Control-Allow-Methods: GET
  Access-Control-Allow-Origin: *

The position of a filter within the filter chain matters. The appropriate position depends on the use case.

When using this filter to enable cross-origin resource sharing (CORS) - place it after uriSecurity filter.

Properties used in the example:

Property Description

enabled

required, default is false

Enables or disables the filter.

class

required

Class that implements AddHeadersFilter.

Access-Control-Allow-Headers

optional

Headers allowed for the request.

Access-Control-Allow-Methods

optional

The HTTP verbs that are allowed to make the request.

See: RFC 7231, section 4: Request methods and RFC 5789, section 2: Patch method.

Access-Control-Allow-Origin

optional

The origin of the request (URL/host).

The wildcard * is used to allow any origin.

HTTP headers and security best practices

In this subsection, we provide some ideas how you can improve security through select HTTP headers.

Content Security Policy (CSP) header

Content Security Policy governs what a web browser (or a user agent, in general) is allowed to load as part of a page. Setting a CSP header allows the creator of a page to control what other resources might be loaded by the underlying HTML or JavaScript code. This is a powerful way to mitigate many Cross-site scripting (XSS) attacks.

You should list – as part of the header value – the origin and all the endpoints required for the page to function. However, if you allow any endpoint that is not within your control, you are opening a hole through which an attack might be staged. Therefore, be extra careful here.

If necessary, we recommend you customize the header to define your own whitelist.

The Vaadin framework performs the CSP check explicitly instead of relying on browser to do so as part of policy execution. You can see official Vaadin statement here.

See also:

Strict-Transport-Security (STS) header

The STS header informs the browser that a page should only be accessed over the HTTPS protocol. The browser will use this knowledge and set all future requests for the same domain to go through HTTPS automatically, thus preventing the extra round trip that might be required otherwise.

Using HTTPS instead of HTTP enables traffic encryption between the page and the client, preventing anyone from intercepting the communication. Using this header is considered more secure than using the 301 redirect on the server when an attempt for the over-the-HTTP access is made.

See also:

X-Content-Type-Options (XCTO) header

XCTO is a marker header that tells the client that the media types (MIME types) advertized as part of the Content-Type headers should be strictly followed and not changed. This helps avoid MIME Type Sniffing.

See also:

X-Frame-Options (XFO) header

Setting the XFO header tells the browser that the given page is not allowed to be embedded in another page. This header setting helps mitigate stealing content, clickjacking (UI redress attack) or allowing malicious sites to pose as the regular ones and fool the users to not check the URLs closely but think instead that they are on a safe page when they are actually not.

See also:

Custom filters

If you need a custom filter, please read Custom filters.

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