What is chaucer criticizing in the pardoners tale?

The Pardoner introduces himself in his prologue. He has no guilt whatsoever; he freely admits to his corruption without the slightest pretense of decency, not even bothering to pay lip service to his religion, which he supposedly serves. Even the moral tale he preaches to the pilgrims is usually preached for monetary gain,

For my exclusive purpose is to win

not at all to castigate their sin.

Once dead what matter how their souls may fare?

They can go blackberrying for all I care!

the Pardoner also brags about committing fraud; he has many false relics and trinkets, which he claims are real, or have magical powers. For instance, he has a sheep's bone which he tells people can be dipped in a well in order to make that well's water an effective snake bite antidote for livestock - for a price, naturally.....Worse than the false relics, however, are the false pardons themselves. The relics are of the saints, which pales in comparison with the pardons, which are of Christ himself. Through crucifixion, Christ bought true pardon for all humanity, which he loved. The Pardoner sells false pardons to people he hates; people he laughs at, deceives, defrauds. Please see below source-link for this excerpt.

He is criticizing the corruption in the church. The Pardoner actually sells pardons, absolving people of their sins. This was blatant and obvious corruption. This was a major issue in the church at the time.