A scorned wife caught her wayward husband where he wasn't supposed to be, with someone he definitely wasn't supposed to be with ... and delivered a double beating, all caught on video.

Security camera video captures the moment a woman surprises her husband at a karaoke bar in a city in Siberia ... as he comes outside, she's waiting for him, and it's a bad tune for him.

Watch the video ... the footage captures the woman slugging her cheating husband multiple times in the face, pulling him by his hood as he tries to fend her off -- that's when his mistress makes her appearance, opening up the door to see what all the fuss is about outside ... and immediately catches hell from the wife.

The enraged woman runs up and unleashes on the wanton harlot with her fists, dragging her by the hair into the street as her husband tries to keep them separated. Shoulda tried harder to do that in the first place, bub.

As the woman breaks away and walks back toward the building, the wife bum-rushes her from behind and smashes her face into the doorframe ... then turns her wrath back on her hubby.

The scene was recorded in Novosibirsk, Russia this week -- the husband reportedly told his wife he was going out of town on business, but apparently stayed behind to spend time with his side piece.

This is all definitely one way to stay warm in a frosty city!!!