Corruptness and corruption are both nouns and mean the same thing: 1. A lack of integrity, dishonesty for personal gain. Both are used to describe the general taking of bribes. 2. Undesirable change. 3. Rottenness, the state of something (meat, vegetable) going bad. However, 'corruptness' would be used more to describe the degree of corruption. It is very seldom used. 'Corruption' is the word most used in such cases.

Corruptness is the state of being corrupt, whereas corruption is the act of corrupting.