Players have discovered a way to partially see through smoke grenades using Molotov cocktails to expose a player's position.
Smoke grenades and molotovs are some of the most important utility items in CS:GO since they're crucial to making crisp rotations and getting clean bomb plants.
A YouTube video posted to the CS:GO subreddit by user Yesber7 shows a player throw a smoke grenade towards another player in a doorway, blocking them from view.
The player then throws a Molotov cocktail into the smoke cloud and lights up an area behind the other player, exposing their outline through the smoke.
The trick is entirely reproducible, as the video shows. This seems to be a legit exploit to partially see through smoke grenades, at least on certain areas of the map.
The effect does disappear when the player who threw the grenade crouches down, but when they stand up the outline is clear as day.
It's unknown whether Valve is aware of the bug or plans to fix it, but users in the Reddit comments seemed to believe it would be unlikely to expect a fix anytime soon.
This kind of exploit seems like something that should be fixed, especially in a highly-competitive game like CS:GO.