Catalysis of the reactions: 25-hydroxycholesterol + O2 + reduced  = 7alpha,25-dihydroxycholesterol + H+ + H2O + oxidized . Also converts (25R)-cholest-5-ene-3beta,26-diol to (25R)-cholest-5-en-3beta,7alpha,26-triol.
CYP7B1 oxysterol 7alpha-hydroxylase activity