Flarum is a forum software for building communities. Flarum's translation system allowed for string inputs to be converted into HTML DOM nodes when rendered. This change was made after v0.1.0-beta.16 (our last beta before v1.0.0) and was not noticed or documented. This allowed for any user to type malicious HTML markup within certain user input fields and have this execute on client browsers. The example which led to the discovery of this vulnerability was in the forum search box. Entering faux-malicious HTML markup, such as <script>alert('test')</script> resulted in an alert box appearing on the forum. This attack could also be modified to perform AJAX requests on behalf of a user, possibly deleting discussions, modifying their settings or profile, or even modifying settings on the Admin panel if the attack was targetted towards a privileged user. All Flarum communities that run flarum v1.0.0 or v1.0.1 are impacted. The vulnerability has been fixed and published as flarum/core v1.0.2. All communities running Flarum v1.0 have to upgrade as soon as possible to v1.0.2.
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
| Link | Tags |
|---|---|
| https://github.com/flarum/core/security/advisories/GHSA-5qjq-69w6-fg57 | third party advisory |
| https://github.com/flarum/core/commit/440bed81b8019dff00642c8f493b4909d505a28a | third party advisory patch |
| https://packagist.org/packages/flarum/core | third party advisory product |