Gonzalo Higuain and substitute Karim Benzema also found the net as Jose Mourinho's side, chasing Real's first continental crown since 2002 and 10th European Cup, secured their place in Friday's draw for the last eight.
On a balmy night in the Spanish capital, Real took a deserved lead in the 26th minute when Sami Khedira sent Kaka clear on the left and the Brazilian crossed for Higuain to poke the ball into the net.
They doubled their advantage 10 minutes into the second half after goalkeeper Sergei Chepchugov could only divert Ronaldo's long-range strike on to a post and in and Benzema followed up his own shot to bag Real's third in the 70th minute, moments after coming off the bench.
France striker Benzema, returning from a brief injury layoff, then unselfishly set up Ronaldo, who scored in the 1-1 draw in freezing Moscow in last month's first leg, to tap in his second and Real's fourth in stoppage-time.
It was the Portuguese international's 11th goal in his last seven appearances for Real and his 42nd of the campaign in all competitions.
"It wasn't spectacular but it was a mature display," Mourinho said at a news conference.
"Without doing anything out of this world we managed to dominate and the game was mostly played out in their half," the Portuguese added.
The only team to beat them in Europe's elite club competition during that period were their great local rivals and European champions Barcelona in last season's semi-finals.
"To obtain a result here we had to play our best game and make no mistakes," CSKA coach Leonid Slutski told a news conference.
"We contained them in the first half but we made mistakes and gave them the chance to attack us."
Real join Barca, AC Milan, APOEL Nicosia, Bayern Munich, Benfica, Chelsea and Olympique Marseille in Friday's draw.
