Honest and Open New EPA Science Treatment Act of 2017 or the HONEST Act This bill amends the Environmental Research, Development, and Demonstration Authorization Act of 1978 to prohibit the Environmental Protection Agency (EPA) from proposing, finalizing, or disseminating a covered action unless all scientific and technical information relied on to support the action is the best available science, specifically identified, and publicly available in a manner sufficient for independent analysis and substantial reproduction of research results. Covered actions are risk, exposure, or hazard assessments, criteria documents, standards, limitations, regulations, regulatory impact analyses, or guidance. Personally identifiable information, trade secrets, or commercial or financial information obtained from a person and privileged or confidential must be redacted prior to public availability. The EPA may use an existing website maintained by another federal agency to make the scientific and technical information available.