This is not a huge exploit but sometimes useful when you ran out of Soul Shard in some situation.
Glyph of Drain Soul is a Warlock's minor glyph which sometimes gives you an additional Soul Shard.
The bug is that when it procs, it also gives Soul Shard to you from the mobs that doesn't normally give Soul Shard too.
Found this by accident while doing Culling of Stratholme, spam Drain Soul on zombies. Tested on opposite faction guards and it also works. But doesn't seem work on critters or mobs that appeared as gray to you, but I'm not sure about this one, maybe I'm just unlucky. If anyone got it from gray mobs or critters please tell me.
I don't think this is working as intended because tooltip says "Your Drain Soul ability occasionally creates an additional soul shard." so I don't think it meant for you to get a single Soul Shard out of nothing.
by Pyromancer