This is not an exploit but a very nice trick a rogue can do to capture a flag (assault or defend).
Basic explanation: If only 1 enemy player defends the node flag, sap and immediately start opening the flag. If he trinkets and interrupts you - blind and immediately start opening the flag. Blind and Sap are 10sec, same as the flag opening time. You will assault/defend the node, and would even be able to restealth before he can hit you.
Full explanation: If there is only one defender left near the flag, and he stays close to the flag, so you can position yourself between him and the flag, you can cast Sap on the enemy defender, immediately starting to use the flag (press sap hotkey and immediately right-click the flag).
If he trinkets your sap, let him strike you, and then do the same: blind him and immediately start using the flag (if you just blind him as soon as he trinkets, it can happen that by lag, he will still hit you and interrupt your flag opening, after he's already blinded and you are already using the flag, thus failing the trick).
Since Sap/blind are 10sec disables and opening flag takes 10 seconds, it always works, except if the class can remove your CC. The classes that it wont work 100% times against are:
Hunter(if he has pet, or he's a BM with trinket), Warlock (if he has pet), Mage (if he has both iceblock and trinket off cooldown), Paladin (if he has both bubble and trinket off cooldown), Warrior (if he has trinket off cooldown and stays in berserker stance), Druid(if he is in form and has trinket off cooldown), Shaman (if he has trinket off cooldown, and had put a searing totem very far away from the flag, if the totem is near the flag, its still doable. You sap the shaman, immediately right click the totem, and after that when you see that totem was targeted and is attacked by you, start opening flag. this should do it, shama sapped totem destroyed and flag is being opened)
Works 100% on Priests, Rogues, mostly works on Shamans, Druids, Warrior, and all other classes (with some exceptions mentioned above).
Overall, its a freaking fun to annoy people like that. They can do just NOTHING, and you can /lol /rofl on them, take the flag and go stealth, then toy with them if they try to retake flag (sap when they are 8 of 10 seconds through), or just lol if they try to find you (carefull with aoe, though).
PS: If that would be commonsense, there would not be so many stoopid rogues that are opening on me when they find me on defense, instead of sapping and going for the flag. I am seldom found when i def a node in stealth, but even when that happens, they never tried to sap-blind me, always tried to kill. And i never had seen this be done to anyone of my premade (i run premades frequently on Sporeggar - Alliance).