Carrie's the threat.
Saul's a terrorist.We can assume he's spent time in the Middle East, and he has a wife from South Asia or the Middle East. He's utterly terrible at polygraphs and he bailed when the crucial question was asked. Given how much he bends and stretches rules for Carrie, we know he's more oriented to "what's right" than "what's acceptable" and he seems a little unstable (although no more or less than most of his colleagues) especially after his wife leaves him. It would be a very long game to play indeed, but maybe Saul is even the one giving Nezir orders.
Carrie is Lisa Simpson.She's blonde, a jazz fan, and shares Lisa's basic personality even if her politics have changed. Even the ages match up if you use the earliest Simpsons episodes.
David Estes is the mole.This is the classic case of The Untwist. If Estes is not getting paid by Abu Nazir, he certainly should be. He rejected surveillance of Brody. He refused a protection detail for the first CIA asset to see Abu Nazir in years right before that asset was murdered, and he also insisted that that asset take an enormous risk in order to download totally useless information. He let Brody in to see Afsal Hamid, and then rejected the idea that Brody or anyone else might have slipped Hamid a razor blade, and opposed polygraphing everyone who had been in to see Hamid. Then he fired Carrie after learning that she had made a major discovery about Nazir and his agenda. In short, he has stood in the way of Carrie's efforts to foil Nazir's plot at every step of the way. Now let's consider his motives. We know he went through a divorce, apparently a bitter one, and lost custody of his children. An experience like that can be both disillusioning and expensive, either or both of which might be reasons to betray one's country. We also know that he took part in the decision to launch the drone strike that killed the 83 children, and that he was in fact the one who brought in the intel that led to the strike. He also opposed the strike on moral grounds, saying that there was a school there, and that a ground assault would have been preferable. Maybe he feels guilty, which would also provide a reason for him to betray his country. Here, however, is the smoking gun: somehow Nazir knew the identities of those responsible for the drone strike, even though the whole thing was covered up very effectively. That means the mole has to be someone who was in on the strike. Who knew about the drone strike, and was in a position to warn Tom Walker, and earlier warn Raqim Faisel? David Estes was the only person who knew about the drone strike, and the identities of those behind it, and was also involved in tracking Faisel and in the meeting with Walker. Of course, there is the fact that Estes was one of the targets of Nazir's plot; he was in the bunker with Brody in "Marine One." If Estes was willing to die to make the plot succeed, why was Brody even necessary? And if not, why was he there? It's possible, however, that Estes simply didn't know all the details. Perhaps Nazir simply didn't tell him the entire plot, but instead let him believe that Walker's attack was the main one.
Saul is Jason GideonAfter retiring from the FBI's Behavioral Analysis Unit, Gideon joined the CIA after, got married, and lives under a pseudonym due to the sensitive nature of his work, along with breaking from his past traumas. Since Jason Gideon was personal friends with a high CIA official, along with profiling both CIA agents (Secrets and Lies) and terrorists (Lessons Learned) it isn't too much a stretch to think that he might have moved there after leaving the BAU (In Name and Blood).
The Hezbollah leader was a mole.For Abu Nazir. Nazir is a member of Al-Qaeda, which is entirely Sunni Muslim and considers Shi'ites to be evil heretics on a par with Christians. So he'd never cooperate openly with Hezbollah, which is entirely Shi'ite. So he's turned the Hezbollah leader just like he turned Brody, and is using him to manipulate Hezbollah for his own ends. All the other Hezbollah members are ignorant of this, and don't know that Nazir is a Sunni or belongs to Al-Qaeda. They just think he's a Shi'ite bigwig.
Even with the concrete evidence of Brody's turn, he's going to get freed anyway.Now granted, this troper gets all his info about Homeland from here and other sites, so I could be off, but I get the feeling that someone within the government is going to try to get rid of the confession tape. Ironically, they WON'T be working for Abu Nazir, and just be attempting to use Brody for their own gain. Though I might be wrong, so Forget About It.
Jessica had a hunch that Brody was/is a terroristIt isn't too far fetched that she's backed into a corner anyhow, Brody's ability in shrouding mental trauma dwindles when unconscious, he physically hurt Jessica and probably whispered taunting threats.
Brody's method of attaining the Vice-PresidencyThe current Vice-President, Walden, is dead as of "Broken Hearts". According to the rules of succession to the office, the President can nominate a replacement to the office to be confirmed by both houses of Congress. So Brody could easily worm his way into the Veep spot even if the CIA doesn't want him there.
Galvez is the mole.I can't really see it as being anyone else. He's not a driving character, but we're more familiar with him than the rest of Carrie's lesser-known assistants. He gets a suspiciously large chunk of screen time for a character with no bearing on the plot, we don't really know who he is, and they did throw us that shootout red herring. He's a terrorist mole after all, it's not like he's afraid of being shot/dying. Also, heroically coming back just in time to "save Carrie" just after his absence may have led to a huge operation that puts Abu Nazir in the CIA's sights? Please.
This show shares a universe with The Blacklist, and Mike Faber is secretly the mastermind of everythingAnd that includes the stuff on that show, too, where he's masquerading as an FBI agent named Dickweed, er, Ressler, which is probably how he really found out about Leo's backstory. And he's gonna give out all kinds of useless intel to get everyone scrambled so he can get his plan achieved. At least until James Spader literally bites his head off in an epic fit of Chewing the Scenery...
Saul's grand planHe plans to have Javadi become the next Iranian President. With what amounts to a puppet regime in place in the Iranian executive, he can force a rapprochement between Iran and Israel, and also perhaps cause Javadi to initiate cultural shifts that restore the kind of secularization that last prevailed in the 1950s.
The new analyst will end up throwing an unexpected monkey wrench into Saul's grand planSaul's been way too focussed on Senator Lockhart, presumptive new director of the CIA, plus keeping his buddy Dar Adal from getting too curious (before the time was right for the reveal) regarding the plan to turn Javadi and reinsert him into the Iranian government.