Laminas-diactoros Cross-site Scripting

laminas-diactoros is a PHP package containing implementations of the PSR-7 HTTP message interfaces and PSR-17 HTTP message factory interfaces. Applications that use Diactoros, and are either not behind a proxy, or can be accessed via untrusted proxies, can potentially have the host, protocol, and/or port of a `Laminas\Diactoros\Uri` instance associated with the incoming server request modified to reflect values from `X-Forwarded-*` headers. Such changes can potentially lead to XSS attacks (if a fully-qualified URL is used in links) and/or URL poisoning. Since the `X-Forwarded-*` headers do have valid use cases, particularly in clustered environments using a load balancer, the library offers mitigation measures only in the v2 releases, as doing otherwise would break these use cases immediately. Users of v2 releases from 2.11.1 can provide an additional argument to `Laminas\Diactoros\ServerRequestFactory::fromGlobals()` in the form of a `Laminas\Diactoros\RequestFilter\RequestFilterInterface` instance, including the shipped `Laminas\Diactoros\RequestFilter\NoOpRequestFilter` implementation which ignores the `X-Forwarded-*` headers. Starting in version 3.0, the library will reverse behavior to use the `NoOpRequestFilter` by default, and require users to opt-in to `X-Forwarded-*` header usage via a configured `Laminas\Diactoros\RequestFilter\LegacyXForwardedHeaderFilter` instance. Users are advised to upgrade to version 2.11.1 or later to resolve this issue. Users unable to upgrade may configure web servers to reject `X-Forwarded-*` headers at the web server level. (2022-08-01, CVE-2022-31109)

Cross site scripting is an attack where a web page executes code that is injected by an adversary. It usually appears, when users input is presented. This attack can be used to impersonate a user, take over control of the session, or even steal API keys.

The attack can be executed e.g. when you application injects the request parameter directly into the HTML code of the page returned to the user:

https://server.com/confirmation?message=Transaction+Complete

what results in:

<span>Confirmation: Transaction Complete</span>

In that case the message can be modified to become a valid Javascript code, e.g.:

https://server.com/confirmation?message=<script>dangerous javascript code here</script>

and it will be executed locally by the user's browser with full access to the user's personal application/browser data:

<span>Confirmation: <script>dangerous javascript code here</script></span>