The "Cross-Boundary Wildfire Solutions Act" mandates the Comptroller General of the United States to conduct a comprehensive study on wildfire mitigation efforts that span across Federal and non-Federal land ownership boundaries. This study will specifically identify existing Federal programs, rules, and authorities that either facilitate or hinder effective cross-boundary wildfire mitigation. Furthermore, the study will evaluate whether modifications to these identified programs or rules could enhance the capacity or access to funding for Federal land management agencies, the Secretary of Agriculture, the Secretary of Homeland Security, States, local governments, and Tribal governments in their wildfire mitigation endeavors. It will also examine activities under the Healthy Forests Restoration Act of 2003, assessing their efficacy and impact on funding access for mitigation. Within two years of enactment, the Comptroller General is required to submit a detailed report to Congress. This report will include the full results of the study and provide specific recommendations to simplify cross-boundary wildfire mitigation processes between Federal agencies and State, local, and Tribal governments.