Natural Law and Theft According to the Catholic Church: the Summa Theologica of Thomas Aquinas

  In case of need all things are common property, so that there would seem to be no sin in taking another's property, for need has made it common.
  ... Hence whatever certain people have in superabundance is due, by natural law, to the purpose of succoring the poor. ... ...it is lawful for a man to succor his own need by means of another's property, by taking it either openly or secretly; nor is this properly speaking theft or robbery.
  ...
  It is not theft, properly speaking, to take secretly and use another's property in a case of extreme need: because that which he takes for the support of his life becomes his own property by reason of that need.
  In a case of a like need a man may also take secretly another's property in order to succor his neighbor in need.

Summa Theologica, IIa IIae q. 66 a. 7.

(Aquinas, Thomas, Summa Theologica, trans. Fathers of the English Dominican Province, New York: Benziger Brothers, 1918, pt. 2, 2nd pt., q. 47-79, pp. 232,233.)