The Prison Officers Association (POA) said Hashem Abedi – the brother of Salman Abedi – threw hot cooking oil over the guards before stabbing them with homemade weapons.
He was sentenced in 2020 to at least 55 years in prison after being found guilty of 22 counts of murder over the 2017 atrocity.
The three officers were taken to hospital after the attack at Frankland prison, in County Durham, shortly before 11am on Saturday.
A female officer is understood to have now been discharged.
Justice Secretary Shabana Mahmood said on X: “I am appalled by the attack of three brave officers at HMP Frankland today. My thoughts are with them and their families.
“The police are now investigating. I will be pushing for the strongest possible punishment. Violence against our staff will never be tolerated.”
Twenty-two people were killed when Salman Abedi detonated a bomb as people were leaving an Ariana Grande concert at the venue.
He died in the attack, while hundreds of others were injured.
Hashem Abedi was found guilty by a jury of 22 counts of murder, attempted murder and plotting to cause an explosion likely to endanger life.
He helped source, buy, stockpile and transport the components for his brother’s bomb, jurors previously heard, using a number of phones, vehicles and addresses in preparation for the attack.
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