Janabah nullifies wiping over leather socks. Consensus has been quoted over this by Ibn Qudamah and al-Nawawi.
Secondly: Removing a Sock or Showing Part of the Foot
Scholars have differed over whether or not removing the leather socks or one of the feet showing nullifies wiping, and this is according to two views:
The first: is that removing the leather socks or showing some of what must be washed from the foot  Hanafis and Malikis hold the position that most of the foot showing nullifies wiping, while Shafi`is and Malikis believe it to be nullified when some of what must be washed of the foot shows. nullifies wiping.  The majority, Hanafis, Malikis, and Shafi`is according to that which is most correct, have opined that he must wash his feet, whereas the Hanbalis said that he should resume with ablution. This is by agreement of the four schools of jurisprudence.
The second: is that removing the leather socks or showing some of what must be washed from the foot does not nullify wiping. Rather, the person who takes his leather socks off may pray and there is nothing upon them as long as they do not become in a state of hadath. This is the position of the Zahiris, a group of the Salaf, and the choice of Ibn Taymiyyah and Ibn `Uthaymin.
Thirdly: The End of the Duration
The ending of the duration for wiping does not nullify purity, and the person may still pray as long as they do not become in a state of hadath. This is the position of the Zahiris, as well as the choice of Ibn al-Mundhir, al-Nawawi, Ibn Taymiyyah, and Ibn `Uthaymin.