On this page of the guide to Back 4 Blood, you will find out what the Corruption Cards are, how they work, and whether the player has any influence on them.
Corruption Cards are cards that appear before you choose which cards you want to keep to receive a specific profit. These cards are sort of specific hindrances that you will have to face. They introduce all kinds of effects. They can affect the weather, limiting your field of view, but they can also affect various modifiers for zombies. They can cause more damage, or, for example, summon other types of zombies.
In spite of certain difficulties, these cards also offer the fulfilment of certain objectives. If the team meets the conditions that are described on the Corruption Cards, then they will receive CP, which can be spent in the store. The store is located in safe rooms. It's always worth to get to know the Corruption Cards before starting a given level.