v3.25.2
Cover Page - USD ($)
$ / shares in Units, $ in Millions
 12 Months Ended
Jun. 30, 2025
Sep. 18, 2025
Dec. 31, 2024
Cover [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Annual Report true    
Document Transition Report false    
Entity Registrant Name CFSB Bancorp, Inc.    
Document Period End Date Jun. 30, 2025    
Title of 12(b) Security Stock, Par Value $0.01 Common Per Share    
Document Fiscal Year Focus 2025    
Security Exchange Name NASDAQ    
Document Fiscal Period Focus FY    
Current Fiscal Year End Date --06-30    
Entity Central Index Key 0001879103    
Entity File Number 001-41220    
Entity Tax Identification Number 87-4396534    
Entity Incorporation, State or Country Code X1    
Entity Address, Address Line One 15 Beach Street    
Entity Address, City or Town Quincy    
Entity Address, State or Province MA    
Entity Address, Postal Zip Code 02170    
City Area Code 617    
Local Phone Number 471-0750    
Entity Current Reporting Status Yes    
Trading Symbol CFSB    
Entity Interactive Data Current Yes    
Entity Filer Category Non-accelerated Filer    
Entity Shell Company false    
Entity Emerging Growth Company true    
Entity Public Float     $ 17.4
ICFR Auditor Attestation Flag false    
Entity Ex Transition Period false    
Entity Common Stock, Shares Outstanding   6,548,575  
Entity Listing, Par Value Per Share $ 0.01    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Small Business true    
Auditor Firm Id 392    
Auditor Name Wolf & Company, P.C    
Auditor Location Boston, Massachusetts    
Document Financial Statement Error Correction [Flag] false    
Auditor Opinion

Opinion on the Consolidated Financial Statements

We have audited the accompanying consolidated balance sheets of CFSB Bancorp, Inc. and subsidiaries (the Company) as of June 30, 2025 and 2024, the related consolidated statements of operations, comprehensive income, changes in stockholders' equity, and cash flows for the years then ended and the related notes (collectively, “the financial statements”). In our opinion, the financial statements present fairly, in all material respects, the financial position of the Company as of June 30, 2025 and 2024, and the results of its operations and its cash flows for the years then ended in conformity with accounting principles generally accepted in the United States of America.