The Cowboys also re-signed Vince Agnew and placed him on the practice squad.
Schaefering played for defensive coordinator Rob Ryan in Cleveland. He had 72 tackles in 37 games from 2009-11 but was cut by the Browns on Aug. 31.
With Brent on the reserve non-football injury list, the Cowboys needed to add depth to the defensive line. As it stands, nose tackle Jay Ratliff is doubtful for the game against the Pittsburgh Steelers with a groin injury.