Pirates were bound to land ashore and breach HBO's walls, to find a way and leak House of the Dragon online.
Many moons ago, HBO found itself the victim of malicious leakers who'd stop at nothing to reap and rave its database in search for scenes and even entire episodes of Game of Thrones way before they went on air. One of the show's directors, David Nutter, even went as far as to tell fans to stay away from the "unfinished" episodes that found their way online as they're not representative of the final product.
Although House of the Dragon hadn't had such issues for its first nine episodes despite its immediate success, it appears that the scum of the internet was biding their time.
HBO confirmed in a statement sent to IGN that the House of the Dragon Season 1 finale is available online, courtesy of pirates, two days ahead of its scheduled premiere this Sunday, October 23.

