# Class CsrfPreventionFilter

java.lang.Object
org.apache.catalina.filters.FilterBase
org.apache.catalina.filters.CsrfPreventionFilterBase
org.apache.catalina.filters.CsrfPreventionFilter

All Implemented Interfaces:
  `Filter`

public class CsrfPreventionFilter extends CsrfPreventionFilterBase
Provides basic CSRF protection for a web application. The filter assumes that:

- The filter is mapped to /*
- `HttpServletResponse.encodeRedirectURL(String)` and `HttpServletResponse.encodeURL(String)` are used to encode all URLs returned to the client

CSRF protection is enabled by generating random nonce values which are stored in the client's HTTP session. Each URL encoded using `HttpServletResponse.encodeURL(String)` has a URL parameter added which, when sent to the server in a future request, will be checked against this stored set of nonces for validity.

Some URLs should be accessible even without a valid nonce parameter value. These URLs are known as "entry points" because clients should be able to "enter" the application without first establishing any valid tokens. These are configured with the `entryPoints` filter `init-param`.

Some URLs should not have nonce parameters added to them at all

- ## Nested Class Summary

  Nested Classes
  Modifier and Type
  Class
  Description
  `protected static class`
  `CsrfPreventionFilter.CsrfResponseWrapper`
  Wrapper for `HttpServletResponse` that adds CSRF nonces to encoded URLs.
  `protected static class`
  `CsrfPreventionFilter.LruCache<T>`
  Despite its name, this is a FIFO cache not an LRU cache.
  `protected static class`
  `CsrfPreventionFilter.MimePredicate`
  A no-nonce Predicate that evaluates a MIME type instead of a URL.
  `protected static interface`
  `CsrfPreventionFilter.NonceCache<T>`
  Interface for a cache of nonces used for CSRF protection.
  `protected static class`
  `CsrfPreventionFilter.PatternPredicate`
  A no-nonce Predicate that matches a regular expression.
  `protected static class`
  `CsrfPreventionFilter.PrefixPredicate`
  A no-nonce Predicate that matches a prefix.
  `protected static class`
  `CsrfPreventionFilter.SuffixPredicate`
  A no-nonce Predicate that matches a suffix.

- ## Field Summary

  ### Fields inherited from class FilterBase

  `sm`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `CsrfPreventionFilter()`
  Default constructor.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `protected CsrfPreventionFilter.NonceCache<String>`
  `createNonceCache(HttpServletRequest request, HttpSession session)`
  Create a new `CsrfPreventionFilter.NonceCache` and store in the `HttpSession`.
  `protected static Predicate<String>`
  `createNoNoncePredicate(ServletContext context, String pattern)`
  Creates a predicate that can match the specified type of pattern.
  `protected static Collection<Predicate<String>>`
  `createNoNoncePredicates(ServletContext context, String patterns)`
  Creates a collection of matchers from a comma-separated string of patterns.
  `void`
  `doFilter(ServletRequest request, ServletResponse response, FilterChain chain)`
  The `doFilter` method of the Filter is called by the container each time a request/response pair is passed through the chain due to a client request for a resource at the end of the chain.
  `protected boolean`
  `enforce(HttpServletRequest req, String requestedPath)`
  Check to see if the request and path should be enforced or only observed and reported.
  `protected CsrfPreventionFilter.NonceCache<String>`
  `getNonceCache(HttpServletRequest request, HttpSession session)`
  Obtain the `CsrfPreventionFilter.NonceCache` associated with the request and/or session.
  `void`
  `init(FilterConfig filterConfig)`
  Iterates over the configuration parameters and either logs a warning, or throws an exception for any parameter that does not have a matching setter in this filter.
  `boolean`
  `isEnforce()`
  Gets the flag to enforce CSRF protection or just log failures as DEBUG messages.
  `void`
  `setEnforce(boolean enforce)`
  Sets the flag to enforce CSRF protection or just log failures as DEBUG messages.
  `void`
  `setEntryPoints(String entryPoints)`
  Entry points are URLs that will not be tested for the presence of a valid nonce.
  `void`
  `setNonceCacheSize(int nonceCacheSize)`
  Sets 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.
  `void`
  `setNonceRequestParameterName(String parameterName)`
  Sets the request parameter name to use for CSRF nonces.
  `void`
  `setNoNonceURLPatterns(String patterns)`
  Sets the list of URL patterns to suppress nonce-addition for.
  `protected boolean`
  `skipNonceCheck(HttpServletRequest request)`
  Determine whether the nonce check should be skipped for the given request.
  `protected boolean`
  `skipNonceGeneration(HttpServletRequest request)`
  Determines whether a nonce should be created.

  ### Methods inherited from class CsrfPreventionFilterBase

  `generateNonce, getDenyStatus, getLogger, getRequestedPath, isConfigProblemFatal, setDenyStatus, setRandomClass`

  ### Methods inherited from class Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

  ### Methods inherited from interface Filter

  `destroy`

- ## Constructor Details

  - ### CsrfPreventionFilter

    public CsrfPreventionFilter()
    Default constructor.

- ## Method Details

  - ### setEntryPoints

    public void setEntryPoints(String entryPoints)
    Entry points are 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 navigating away from it. Entry points will be limited to HTTP GET requests and should not trigger any security sensitive actions.
    Parameters:
      `entryPoints` - Comma separated list of URLs to be configured as entry points.

  - ### setNonceCacheSize

    public void setNonceCacheSize(int nonceCacheSize)
    Sets 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.
    Parameters:
      `nonceCacheSize` - The number of nonces to cache

  - ### setNonceRequestParameterName

    public void setNonceRequestParameterName(String parameterName)
    Sets the request parameter name to use for CSRF nonces.
    Parameters:
      `parameterName` - The request parameter name to use for CSRF nonces.

  - ### setEnforce

    public void setEnforce(boolean enforce)
    Sets the flag to enforce CSRF protection or just log failures as DEBUG messages.
    Parameters:
      `enforce` - `true` to enforce CSRF protection or `false` to log DEBUG messages and allow all requests.

  - ### isEnforce

    public boolean isEnforce()
    Gets the flag to enforce CSRF protection or just log failures as DEBUG messages.
    Returns:
      `true` if CSRF protection will be enforced or `false` if all requests will be allowed and failures will be logged as DEBUG messages.

  - ### setNoNonceURLPatterns

    public void setNoNonceURLPatterns(String patterns)
    Sets the list of URL patterns to suppress nonce-addition for. Some URLs do not need nonces added to them such as static resources. By not adding nonces to those URLs, HTTP caches can be more effective because the CSRF prevention filter won't generate what look like unique URLs for those commonly-reused resources.
    Parameters:
      `patterns` - A comma-separated list of URL patterns that will not have nonces added to them. Patterns may begin or end with a `*` character to denote a suffix-match or prefix-match. Any matched URL will not have a CSRF nonce added to it when passed through `HttpServletResponse.encodeURL(String)`.

  - ### createNoNoncePredicates

    protected static Collection<Predicate<String>> createNoNoncePredicates(ServletContext context, String patterns)
    Creates a collection of matchers from a comma-separated string of patterns.
    Parameters:
      `context` - the Servlet context
      `patterns` - A comma-separated string of URL matching patterns.
    Returns:
      A collection of predicates representing the URL patterns.

  - ### createNoNoncePredicate

    protected static Predicate<String> createNoNoncePredicate(ServletContext context, String pattern)
    Creates a predicate that can match the specified type of pattern.
    Parameters:
      `context` - the Servlet context
      `pattern` - The pattern to match e.g. `*.foo` or `/bar/*`.
    Returns:
      A Predicate which can match the specified pattern, or `null` if the pattern is null or blank.

  - ### init

    public void init(FilterConfig filterConfig) throws ServletException
    Description copied from class: `FilterBase`
    Iterates over the configuration parameters and either logs a warning, or throws an exception for any parameter that does not have a matching setter in this filter.
    Specified by:
      `init` in interface `Filter`
    Overrides:
      `init` in class `CsrfPreventionFilterBase`
    Parameters:
      `filterConfig` - The configuration information associated with the filter instance being initialised
    Throws:
      `ServletException` - if `FilterBase.isConfigProblemFatal()` returns `true` and a configured parameter does not have a matching setter

  - ### doFilter

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException
    Description copied from interface: `jakarta.servlet.Filter`
    The `doFilter` method of the Filter is called by the container each time a request/response pair is passed through the chain due to a client request for a resource at the end of the chain. The FilterChain passed in to this method allows the Filter to pass on the request and response to the next entity in the chain.

    A typical implementation of this method would follow the following pattern:-
    1. Examine the request
    2. Optionally wrap the request object with a custom implementation to filter content or headers for input filtering
    3. Optionally wrap the response object with a custom implementation to filter content or headers for output filtering
    4. a) Either invoke the next entity in the chain using the FilterChain object (`chain.doFilter()`),
    4. b) or not pass on the request/response pair to the next entity in the filter chain to block the request processing
    5. Directly set headers on the response after invocation of the next entity in the filter chain.

    Parameters:
      `request` - The request to process
      `response` - The response associated with the request
      `chain` - Provides access to the next filter in the chain for this filter to pass the request and response to for further processing
    Throws:
      `IOException` - if an I/O error occurs during this filter's processing of the request
      `ServletException` - if the processing fails for any other reason

  - ### enforce

    protected boolean enforce(HttpServletRequest req, String requestedPath)
    Check to see if the request and path should be enforced or only observed and reported. Note that the `requestedPath` parameter is purely a performance optimization to avoid calling `CsrfPreventionFilterBase.getRequestedPath(HttpServletRequest)` multiple times.
    Parameters:
      `req` - The request.
      `requestedPath` - The path of the request being evaluated.
    Returns:
      `true` if the CSRF prevention should be enforced, `false` if the CSRF prevention should only be logged in DEBUG mode.

  - ### skipNonceCheck

    protected boolean skipNonceCheck(HttpServletRequest request)
    Determine whether the nonce check should be skipped for the given request.
    Parameters:
      `request` - The HTTP servlet request
    Returns:
      `true` if the nonce check should be skipped

  - ### skipNonceGeneration

    protected boolean skipNonceGeneration(HttpServletRequest request)
    Determines whether a nonce should be created. This method is provided primarily for the benefit of subclasses that wish to customise this behaviour.
    Parameters:
      `request` - The request that triggered the need to potentially create the nonce.
    Returns:
      `true` if a nonce should be created, otherwise `false`

  - ### createNonceCache

    protected CsrfPreventionFilter.NonceCache<String> createNonceCache(HttpServletRequest request, HttpSession session)
    Create a new `CsrfPreventionFilter.NonceCache` and store in the `HttpSession`. This method is provided primarily for the benefit of subclasses that wish to customise this behaviour.
    Parameters:
      `request` - The request that triggered the need to create the nonce cache. Unused by the default implementation.
      `session` - The session associated with the request.
    Returns:
      A newly created `CsrfPreventionFilter.NonceCache`

  - ### getNonceCache

    protected CsrfPreventionFilter.NonceCache<String> getNonceCache(HttpServletRequest request, HttpSession session)
    Obtain the `CsrfPreventionFilter.NonceCache` associated with the request and/or session. This method is provided primarily for the benefit of subclasses that wish to customise this behaviour.
    Parameters:
      `request` - The request that triggered the need to obtain the nonce cache. Unused by the default implementation.
      `session` - The session associated with the request.
    Returns:
      The `CsrfPreventionFilter.NonceCache` currently associated with the request and/or session