Cash, 32, hit .204 with two homers and four RBI for the Astros this season before being designated for assignment on June 23rd.
The acquisition was prompted by an injury to team captain Jason Varitek, reportedly a broken bone in his foot that will cause him to miss four to six weeks.
Cash spent part of the 2007 and 2008 with the Sox, hitting .207.
He caught Tim Wakefield 35 times during his tenure with the Red Sox, thus explaining why the club may have re-acquired him in the wake of Victor Martinez’ injury.
With Wakefield due to start tomorrow night, Cash could be added to the roster prior to game time.