Tightening up the defensive issues the main focus this week
Leinster's defence coach Kurt McQuilkin is sure to have had plenty of sleepless nights this week as he tries to come to terms with how his side managed to concede three tries against a hapless Treviso outfit.
The week before, Leinster shipped another three, albeit to far superior opposition in Ulster, but for a team who have prided themselves on their defensive capabilities this season, major improvements are needed for next Friday's semi-final clash.
Leinster's meeting with Ulster will see the Pro12's two best defences go head-to-head with the Blues having conceded just two fewer tries (27) than their northern rivals (29).
In contrast to Connacht who finished level on points (73) with Leinster, Pat Lam's side leaked 46 tries which is more than any side in the top four and indeed 10 more than Munster who finished back in sixth.
Leinster's attack has yet to really fire on all cylinders this season but Johnny Sexton's try last week was a clear indicator that they are still more than capable of tearing defences to shreds with a perfectly executed pre-planned move.
Few would argue that the squad at Cullen's disposal is stronger than anyone else's in the league but they will be desperate to shore up their defence against an in-form Ulster side whose backline is a serious threat.
"It was quite nice to get in and score a few tries," Cullen reflected after his side eased passed Treviso.
"It was a bit disappointing the last 17, 18 minutes in giving up three tries but there is always a tendency to manage themselves through that last part of the game. Treviso fought to the very end and they take some credit for that.
"I just think we have to deal with what we can control and we did that pretty well for the most part. It's a totally different challenge now. It's dust ourselves off and get ready for the final push but it is great to be still in the mix at this time of year.
"It (30-6 defeat two weeks ago) will be fresh. There are a lot of learnings for us from the last week that we can be better at but Ulster are a very good team as well. It will be another very tough day."
Ulster's convincing win in Belfast means that they won't fear travelling to the RDS but Leinster have a point to prove and with a place in the final at stake, in front of a packed house, motivation will not be in shortly supply.
Les Kiss' men haven't won a trophy since the old Celtic League in 2006 but their Ireland flanker Chris Henry believes that they have learned from the shortcomings that cost them silverware in recent seasons.
"Every time you play (another) province, people say you know them inside out and that is the case," Henry said.
"There's a lot at stake for both teams. Leinster have been in finals, they've won big games but we've won down there before.
"I think ourselves and Leinster are coming into form now. We need cool heads to go with that intensity and physicality.
"They're all boxes that have to be ticked but I'm sure it'll be a cracking game of rugby and I'm itching to go already."