The most common and most likely answer to this crossword clue is the 6 letter word VILIFY
I've seen this crossword clue in Financial Times
V
I
L
I
F
Y
More clues leading to the result VILIFY
Buddy explains!

The straight part
We know that "Malign" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case malign = vilify.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does VILIFY mean?
VILIFY verb- To say defamatory things about someone or something; to speak ill of.
- To belittle through speech; to put down.