Nine shots from an automatic weapon were fired through the front patio door of a house at Hyde Rd, while a couple were asleep upstairs.
The attack was carried out at around 4am on Saturday.
The scene was cordoned off and door-to-door inquiries are ongoing in the area.
Gardaí suspect the attack is drugs related.
One source said: “Various groups who worked under the control of the McCarthy-Dundon gang have now gone out on their own and they are each trying to carve out their own areas.
“This has led to various turf-war situations in the city and in the county where there have also been a number of drugs-related violent incidents.”
All but one of the key figures in the McCarthy-Dundon gang, which operated out of the Ballinacurra Weston area, are now serving long jail sentences.
One of the gang leaders, known as Mr Big, who gardaí suspect was involved in the murder of nightclub bouncer Brian Fitzgerald, is still living and running a drugs operation in the city.
Mr Fitzgerald was shot dead in November 2002 after he arrived home in Corbally from his job as head of security at a city-centre nightclub.
James Martin Cahill and Gary Campion are serving life sentences for his murder.
Cahill was a hired gunman driven to and from the murder by notorious Limerick criminal Gary Campion.
The murder was ordered by Mr Big, who still runs a drugs operation from the Ballinacurra Weston area.
He engaged a Co Clare associate to organise the murder of Mr Fitzgerald, who had made a complaint to the gardaí that Mr Big had threatened to kill him over blocking drugs at the nightclub he worked at.
Mr Big had a suspended jail sentence hanging over him and feared if Mr Fitzgerald proceeded with his complaint a conviction would lead to the activation of the sentence.
Following the murder, Mr Big left for England where he was caught up in trading in high-powered guns, for which he served a significant jail term in Britain.