Close Official Acts Loophole Act of 2017 This bill amends the federal criminal code to modify the definition of "official act" for purposes of an offense involving bribery of public officials. Bribery of public officials includes offering a thing of value to (or acceptance of a thing of value by) a public official to influence an official act (or in return for being influenced in connection with an official act). Currently, an official act is any decision or action on a question, matter, cause, suit, proceeding, or controversy, which may at any time be pending, or which may by law be brought before a public official, in their official capacity. This bill broadens an official act to include the personal and substantial participation through, or investigation of, a question, matter, cause, suit, proceeding, or controversy.