The Attorney-General's Department has been asked to look at whether any laws were broken in Scott Morrison's leaking of confidential information from cabinet and its national security committee to journalists.
The book Plagued, written by journalists Simon Benson and Geoff Chambers, contains detailed information about how Mr Morrison as prime minister dealt with the COVID-19 pandemic.
It also includes a number of security challenges including China, nuclear submarines and the Russian invasion of Ukraine.
Labor senator Tony Sheldon asked officials from the Department of Prime Minister and Cabinet on Friday what steps were being taken to deal with what appeared to be cabinet leaks.
The deliberations of cabinet and its various committees are ordinarily considered confidential.
Acting deputy secretary John Reid said his department was not aware at the time that Mr Morrison had been briefing reporters about cabinet matters.
Mr Reid said the department had reviewed the book and concluded it appeared to contain disclosures from cabinet and cabinet committees.
"Our conclusions were that it certainly appears to reveal information that is, or was until revealed, cabinet material and would ordinarily be protected under the principle of cabinet confidentiality," he said.
Asked whether disclosures about discussions on national security matters such as nuclear submarines and Russia's invasion of Ukraine could harm Australia's interests, Mr Reid said: "It may, senator."
Mr Reid said there was a longstanding convention on the confidentiality of cabinet and cabinet deliberations.
"(But) of course the prime minister of the day always reserves the prerogative to disclose or release information from cabinet meetings," Mr Reid told the Senate estimates hearing.
He said it had been referred to the Attorney-General's Department because that agency was responsible for any possible criminal action relating to disclosures.
Liberal senator Michaelia Cash declined to say whether it was appropriate for national security information to be leaked from cabinet and whether she was aware of the leaks.
Asked whether she was concerned about the level of information in the public domain, the former attorney-general said: "I am incredibly proud of the achievements of the former coalition government."
She said Australians were instead concerned with the cost of living.
"I'm out there talking to people in the street. That's what they're raising with me, not the issue that you are raising," she told AAP.
Mr Reid said the review of the book was initiated by media reports suggesting cabinet information when asked whether Prime Minister Anthony Albanese's office had asked for an investigation.
"It seemed appropriate we should have a look at it," he said.
It is highly unlikely action would be taken against either of the journalists, but Mr Morrison could receive a "please explain" letter.
Mr Morrison is also the subject of an inquiry by former High Court judge Virginia Bell after it was revealed he had secretly appointed himself to five ministries.
The solicitor-general found Mr Morrison did not break any laws in secretly taking on the portfolios between 2020 and 2021, but that it went against the principles of "responsible government".
The Bell report will be handed down on November 25.
