The 22-year-old has made three first-team appearances for Boro and has also spent previous loan spells with Darlington, Barnsley, Bradford City and Crewe Alexandra in the last four seasons.
"We've been tracking Ross all summer and we're really pleased to have secured his services for the season," said Bluebirds chairman Peter Ridsdale .
"Ross is known to be one of the bright young keepers coming through and we're glad that our patience has paid off.
"The signing of another keeper will really give us genuine competition in all positions and that's what we set out to achieve during the summer."