Home-Gallery.org is a self-hosted open-source web gallery to browse personal photos and videos. In 1.15.0 and earlier, an open CORS policy in app.js may allow an attacker to view the images of home-gallery when it is using the default settings. The following express middleware allows any website to make a cross site request to home-gallery, thus allowing them to read any endpoint on home-gallery. Home-gallery is mostly safe from cross-site requests due to most of its pages requiring JavaScript, and cross-site requests such as fetch() do not render javascript. If an attacker is able to get the path of the preview images which are randomized, an attacker will be able to view such a photo. If any static files or endpoints are introduced in the future that contain sensitive information, they will be accessible to an attacker website.
The product uses a web-client protection mechanism such as a Content Security Policy (CSP) or cross-domain policy file, but the policy includes untrusted domains with which the web client is allowed to communicate.
If a cross-domain policy file includes domains that should not be trusted, such as when using wildcards under a high-level domain, then the application could be attacked by these untrusted domains. In many cases, the attack can be launched without the victim even being aware of it.