Secure Adjacent Federal Property Act of 2023 This bill requires an interagency study to help agencies produce a security assessment process for space adjacent to space to be leased for high-security federal activities. Specifically, the bill directs the General Services Administration (GSA), in coordination with the Federal Protective Service, the Department of Homeland Security, the Office of Management and Budget, and any other relevant entities, to carry out a governmentwide study examining options to assist agencies to produce a process to assess the security of adjacent space before entering into a lease or novation agreement for high-security space. The GSA, in coordination with such entities, shall (1) establish a working group to assist in carrying out the study, and (2) report to Congress.