# 3.7.5

* [CVE-2019-19326 Web Cache Poisoning](#CVE-2019-19326)

## CVE-2019-19326 Web Cache Poisoning {#CVE-2019-19326}

Silverstripe sites using HTTP cache headers and HTTP caching proxies (e.g. CDNs) can be susceptible to web cache poisoning through the:
* `X-Original-Url` HTTP header
* `X-HTTP-Method-Override` HTTP header
* `_method` POST variable.

In order to remedy this vulnerability, Silverstripe Framework 3.7.5 removes native support for these features. While this is technically a semantic versioning breakage, these features are inherently insecure and date back to a time when browsers didn't natively support the full range of HTTP methods. Sites who still require these features will have highly unusual requirements that are best served by a tailored solution.

### Re-enabling the support for removed features

These features are best implemented by defining a `RequestFilter`. Request Filters are similar to the more modern concept of "middleware" as defined by the PSR-15 standard and supported by Silverstripe 4.

The following example illustrate how to implement a `RequestFilter` that restore support for the `X-Original-Url` header and the `_method` POST parameter for request originating from a trusted proxy.

```php
<?php

/**
 * This is meant to illustrate how to implement a RequestFilter. It assumes your
 * trusted proxy will strip the insecure data from any requests. If you blindly
 * copy-paste this in in your code base, you'll simply replicate the vulnerability.
 */
class InsecureRequestProcessor implements RequestFilter
{

    public function preRequest(SS_HTTPRequest $request, Session $session, DataModel $model)
    {
        if (TRUSTED_PROXY) {
            $originalUrl = $request->getHeader('X-Original-Url');
            if ($originalUrl) {
                $request->setUrl($originalUrl);
                $_SERVER['REQUEST_URI'] = $originalUrl;
            }

            $methodOverride = $request->postVar('_method');
            $validMethods = ['GET', 'POST', 'PUT', 'DELETE', 'HEAD'];
            if ($methodOverride && in_array(strtoupper($methodOverride), $validMethods)) {
                $request->setMethod($methodOverride);
            }
        }

        return true;
    }

    public function postRequest(SS_HTTPRequest $request, SS_HTTPResponse $response, DataModel $model)
    {
        return true;
    }
}
```

To learn more about re-implementing support for the disabled features:
* read [How to implement a Request Filter](/developer_guides/controllers/requestfilters) on the Silverstripe documentation
* read [how to configure trusted proxies](/developer_guides/security/secure_coding/#request-hostname-forgery) on the Silverstripe documentation
* review [api:RequestFilter] interface

To learn more about middleware:
* read the [PSR-15: HTTP Server Request Handlers](https://www.php-fig.org/psr/psr-15/) standard
* read the [Silverstripe 4 documentation about HTTP Middlewares](https://docs.silverstripe.org/en/4/developer_guides/controllers/middlewares/) standard.

<!--- Changes below this line will be automatically regenerated -->

<!--- Changes above this line will be automatically regenerated -->