A broken link error is displayed after you save HTML code similar to the following example in the Rich Text field HTML Editor:
<img src=''-/media/Default Website/sc_logo''>
To resolve the issue, download and install the patch compatible with the affected product version:
https://github.com/SitecoreSupport/Sitecore.Support.152589/releases
To get a solution for other releases, contact Sitecore Support.