Citizens of both Sudan and South Sudan who were in the U.S. on either November 4, 1997 (for Sudan) or November 3, 2011 (for South Sudan) may have become eligible for -- and hopefully applied for and received -- Temporary Protected Status (TPS). This designation was meant to protect them from ongoing armed conflict and other extraordinarily difficult conditions in those countries.
The TPS designations for Sudan and South Sudan have been regularly renewed, and at each renewal, recipients of TPS must reapply to retain their status and their work permit. In some cases, even people who have neglected to apply up to now may, if they meet the legal criteria, file a late application for TPS.
For details on who is eligible and how to file an application with U.S. Citizenship and Immigration Services (USCIS), see the relevant announcements from the U.S. government, including "DHS Announces 18-Month Extension of Temporary Protected Status for Sudan" and "DHS Announces 18-Month Re-designation and 18-Month Extension of Temporary Protected Status for South Sudan."