Securing Open Source Software Act of 2023 This bill sets forth the duties of the Cybersecurity and Infrastructure Security Agency (CISA) regarding open source software security. Open source software means software for which the human-readable source code is made available to the public for use, study, reuse, modification, enhancement, and redistribution. Specifically, CISA must perform outreach and engagement to bolster the security of open source software; support federal efforts to strengthen open source software security; coordinate with nonfederal entities on efforts to ensure long-term open source software security; serve as a public point of contact regarding open source software security for nonfederal entities; and support federal and nonfederal supply chain security efforts by encouraging efforts to bolster open source software security. CISA must (1) publish a framework, incorporating government, industry, and open source software community frameworks and best practices, for assessing the risk of open source software components; (2) update the framework at least annually; and (3) ensure, to the greatest extent practicable, that the framework is usable by the open source software community. The bill requires CISA to assess open source software components used by federal agencies based on the framework and provides for a pilot assessment of critical infrastructure. CISA's Cybersecurity Advisory Committee may establish a software security subcommittee. The Office of Management and Budget, in coordination with CISA, the Office of the National Cyber Director, and the General Services Administration, shall issue guidance on the responsibilities of the chief information officers at specified agencies regarding open source software.