YouTubers OutsideXbox bring a quick guide to finding the secret Venom X weapon in the Devastation DLC for Call Of Duty: Ghosts.
If you can't watch the video, here's how to unlock the secret weapon. On the "Unearthed" map, there's a large crane with three grey supports on it.
Using a grenade and grenade launcher, blow up those supports, and the crane will drop the cage it's holding up. Inside is the Venom-X weapon, which is a type of sticky grenade launcher. It doesn't have much ammo, but you don't have to drop one of your normal weapons to carry it.
In addition to that, you can hit a button that will cause the crane to lift the cage back up and either get a great vantage point to shoot people from, or become a sitting duck for other enemies.