Is a divorced woman who is currently married obligated to inform her husband about her previous customary marriage, which lasted for one year, or is it permissible for her to conceal it, especially since her husband only knows about her divorce from her first husband?

A woman is not obligated to inform her husband about a void marriage she entered into before their marriage, because this is not one of the defects that invalidate a marriage and must be disclosed to the suitor. However, she must repent to Allah from this void marriage, as it is a forbidden temporary marriage (mut'ah) which renders the marriage null and void from its very inception.