How can an attacker execute malware through a script?

Reddit is  an american  social news  sharing service, web content  rating, and  discussion  website.  the name "reddit" is a  play-on-words  with the phrase "read it",  when items (links or text posts) are submitted to a subreddit, the users, called "redditors",  can vote for or against these links or posts (upvote/downvote).