For last year's postseason (and this year's regular season), the NFL adopted a new sudden death format.
The following approved ruling for a safety on an opening possession states:
A.R. 16.19 SAFETY
Third-and-5 on A7. On the opening possession of overtime, A1 is tackled in his own end zone for a safety.
Ruling: Game over. Team B wins. Both teams have met the minimum requirements for possession.
How has both teams met the minimum requirements for possession in this case? If Team B records a safety, then (given they kicked the ball off to Team A to start overtime) they do not technically ever have possession.
Possession: Actual possession of the ball with complete control. The defense gains possession when it catches, intercepts, or recovers a loose ball.