The extent of attorney-client privilege in legal malpractice depends on the factual setting. One point is the “at issue” principal which allows disclosure of materials that are said to be at issue in the legal malpractice. Another interesting idea is joint defense and privilege between defendants. Here is a recent case on point.
“The same law firm held plaintiff, Beacon, and other named defendants as clients. It opposed, on attorney-client privilege grounds, plaintiff’s motion for documents. In July 2005, the court held that an April 2005, waiver of attorney-client privilege, by Beacon’s liquidator, did not waive the privilege as to the firm’s other clients”