silverstripe-framework/docs/en/04_Changelogs/3.7.5.md

3.7.5

• CVE-2019-19326 Web Cache Poisoning
• CVE-2020-9311 Malicious user profile information can cause login form XSS

CVE-2019-19326 Web Cache Poisoning

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

/**
 * 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 on the Silverstripe documentation
• read how to configure trusted proxies on the Silverstripe documentation
• review [api:RequestFilter] interface

To learn more about middleware:

• read the PSR-15: HTTP Server Request Handlers standard
• read the Silverstripe 4 documentation about HTTP Middlewares standard.

Review the CVE-2019-19326 public disclosure

CVE-2020-9311 Malicious user profile information can cause login form XSS

Malicious users with a valid Silverstripe login (usually CMS access) can craft profile information which can lead to XSS for other users through specially crafted login form URLs.

Review the CVE-2020-9311 public disclosure