Is it possible to have Wikipedia sources in a cycle?

I’m not very familiar with how Wikipedia vets the sources in the references/external links. I was wondering whether there are manual or automated checks for cyclic sources, for example a Wikipedia page cites a source for something, but such source after a few rounds of citing would go back to the same Wikipedia page.

• Does that happen with Wikipedia?
• Does it matter? I presume that would invalidate the source?
• How do they make sure it does not happen? Is there an automated check or something?