The warning of mixture between HTTP and HTTPS contents is a significant security issue.
When you have such warnings that keep popping up from time to time and the end-users are "advised" to ignore such pop up, putting across that it is a benigned behaviour, soon they will
NOT BE ABLE to recognise a MITM attack pop up that is caused by the attack host posing an invalid certificate of the same domain name. That is why such warnings
MUST BE treated with caution and end-users should be notified to either set their browsers to deny access to any NON-HTTPS resources in a HTTPS enabled website, and be advised appropriately to react with skepticism when any form of warnings are produced by the browser to the relevant website.
In my findings, simply using the Developer Tools in Chrome, one can see that such mixture are not limited to user provided contents which are pointing to NON-HTTPS resources.
The main page alone @
https://forums.hardwarezone.com.sg/, already exposed Advertising GIF resources and CSS resources which are fetched via NON-HTTPS conduit in a HTTPS enabled website. This has nothing to do with user contributed contents and should be rectified as soon as possible.
Embedding a NON-HTTPS hyperlink will not cause such issue, since what the forum has been doing to opening up hyperlink in a new window, which will then be out of the HWZ domain.
For end-users contents, they are mostly IMAGES or YOUTUBE links are externally fetched contents displayed in the same domain name as HWZ Forum. YOUTUBE already have HTTPS conduit, so all HWZ need to do is for new YOUTUBE embed, only allow HTTPS link and for existing posts which are already embedded with HTTP link, either sieve though the database and perform a data patch to change all YOUTUBE links to
HTTPS://...., or perform this job at the client end using a Javascript routine, which can be easily performed using tools like jQuery.
For Images, there are still sites like TINYPIC which does not offer HTTPS access, for these sites, deny such access by removing them, or advice the end-users that breakage in not fetching such contents are expected behaviours to enhance the security of the forum. Sites like IMGUR supports HTTPS for the image resources are acceptable and should be enabled. HWZ can list out a couple of such image repository sites to allow end-users to host their images. HWZ can also opt to lock down all images repositories to a limited set to keep things accountable and secure with the use of CSP, at a latter date for the end-users to comply over time, since old posts will eventually be neglected and prune with the least disruption to the service.
Code:
<html>
<head>
<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js"></script>
<script type="text/javascript">
$(function() {
$("img").each(function() {
$(this).attr("src", $(this).attr("src").replace(/^http:\/\//, "https://"))
});
});
</script>
</head>
<body>
<img src='http://i.imgur.com/H0gH9pW.png'>
<img src='http://i.imgur.com/H0gH9pW.png'>
</body>
</html>