There is, it's bad. Luckily votes aren't very crucial.

Votes are crucial. HN goes to great lengths to prevent votes that do not stem from real user intent.

See this post for example:

https://news.ycombinator.com/item?id=22761897

Quotes:

"Voting ring detection has been one of HN's priorities for over 12 years"

"I've personally spent hundreds of hours working on this"