Is there any huge liability? Unfortunately, yes. Thanks to the lawyers and the leeches who will sue anyone to "get rich quick", anyone can be sued today no matter how stupid. If anyone is on your property for any reason-- even to rob it-- and they get hurt because you created a dangerous situation for them, they can sue you. If they fall down your stairs, they can sue you for "slip and fall", etc. It's stupid, and it costs everyone added fees because we all have to pass on the cost, but until we get serious tort reform (something the media seems hell bent on preventing) we will continue to live under this cloud.
You can buy liability insurance. I suspect your current insurance would not cover injuries from a haunted house event. Or you can risk it and do everything you can to make it safe. I ran a haunted house for friends 15 years back and there were no injuries and no law suits. But if someone gets hurt, then yes, they can sue you and if they are a stranger, they will probaby try to do just that. (Even friends do it.) The personal injury lawyers charge NOTHING unless the collect, so people feel they have nothing to lose and a possible jackpot to gain. If you own the house free and clear, or have other assets, then the lawyer is much more likely to sue.
I'm not saying don't do it, but you do need to be aware of the real risks.