I'm flying from NY to Paris, enroute to Cairo. Will I have to go through customs? I have only an hour between flights.

Welcome to Fluther.

I wouldn’t think that you’ll have to clear Customs in Paris, because your bags will most likely be trans-shipped to the new carrier and you’ll spend your layover time in the International Transit Lounge. But not having flown through Orly before—and never having had to clear Customs and Immigration in France at all, in fact—I can’t say for sure. I’m assuming that there’s a single International terminal and you won’t have to handle your own bags.

If you booked the ticket through a travel agent, then it’s a question that they should be able to answer with certainty. In fact, a travel agent might still answer the question for you regardless of where or how you ticketed, because it’s a pretty elementary question.

I’m 95% sure that @CyanoticWasp is correct. Unless there’s some special exception that Paris has for international connections, then you will have to go through customs. As an example, if you were going from Paris to Canada with a stop-over in the US, then you would have to go though US customs for certain.

I wish I could do that!

No, it is assumed that you went through customs and security at your point of origin. You will have to go through customs in Cairo.