c't is a German computer magazine that has been around since the early 80s. It has a very good reputation for journalistic quality, expertise and thoroughness of investigations.
heise is the publisher that owns c't, hence the url.
The bugs are currently exclusive to c't (a German IT magazine closely linked to heise.de) and they could confirm those bugs "in several ways".
[IMO: c't and heise.de are considered both first class sources in Germany]
Technical details won't be published in order to give manufacturers time to respond.
Still, they are a consequence of the same architectural problem as Specter, hence labelled Specter-NG
There are indications that at least some ARM CPUs are vulnerable and AMD CPUs are still being tested.
Intel estimates the risk to be "high" for four and "medium" for another four.
C't itself considers at least one "extremely high" because it would allow for controlling the host system from within a VM, or accessing other VMs on the same system. This was also possible for the original specter bugs but this specific attack would be much easier as it required "much less detailed knowledge".
c't is a German computer magazine that has been around since the early 80s. It has a very good reputation for journalistic quality, expertise and thoroughness of investigations.
heise is the publisher that owns c't, hence the url.