Camaleon CMS vulnerable to stored XSS through user file upload (GHSL-2024-184)

A stored cross-site scripting has been found in the image upload functionality that can be used by normal registered users:
It is possible to upload a SVG image containing JavaScript and it's also possible to upload a HTML document when the format
parameter is manually changed to [documents][1] or a string of an [unsupported format][2]. If an authenticated user or administrator visits that uploaded image or document malicious JavaScript can be executed on their behalf (e.g. changing or deleting content inside of the CMS.)

[1]: https://github.com/owen2345/camaleon-cms/blob/feccb96e542319ed608acd3a16fa5d92f13ede67/app/uploaders/camaleon_cms_uploader.rb#L105-L106
[2]: https://github.com/owen2345/camaleon-cms/blob/feccb96e542319ed608acd3a16fa5d92f13ede67/app/uploaders/camaleon_cms_uploader.rb#L110-L111

## Impact

This issue may lead to account takeover due to reflected Cross-site scripting (XSS).

## Remediation

Only allow the upload of safe files such as PNG, TXT and others or serve all "unsafe" files such as SVG and other files with a content-disposition: attachment header, which should prevent browsers from displaying them.

Additionally, a [Content security policy (CSP)][3] can be created that disallows inlined script. (Other parts of the application might need modification to continue functioning.)

[3]: https://web.dev/articles/csp

To prevent the theft of the auth_token it could be marked with HttpOnly. This would however not prevent that actions could be performed as the authenticated user/administrator. Furthermore, it could make sense to use the authentication provided by Ruby on Rails, so that stolen tokens cannot be used anymore after some time.