Hudhaifah said: “The Messenger of Allah came to a place where a group of people threw their refuse, and he urinated standing up. He (pbuh) then called for water, and wiped over his leather socks (during Wudu). (Sahih)
Squatting to relieve oneself is more commonly reported, this Hadith proves that when there is a reason and genuine need, there is no harm in standing to relieve oneself, provided one does so in a way that they can protect themselves from any splashing of the urine.
(Sunan-Abu-Dawud volume 1, number 23)