I wouldn’t call it a bug, but more an edge case.
No
Within a CDATA section, only the CDEnd string is recognized as markup, so that left angle brackets and ampersands may occur in their literal form; they need not (and cannot) be escaped using “
<” and “&”. CDATA sections cannot nest.
The problem is, after the first <![CDATA[ everything up to the ]]> is considered to be “character data” and not XML tags. Once a ]]> is encountered, it goes back to needing to be well-formed valid XML.
My first thought was to change the < and / or ] to an entity. But after seeing the “and cannot” I guess that won’t work.
Maybe “breaking” the inner CDEnd by inserting zwsp characters would work?
EDIT
The RSS for this topic is valid and uses entities (< and >), so it looks like my first thought should work.