Blues, who were poor in the first half, took the lead through Erik Huseklepp's second goal for the club - a neat close-range finish - shortly after Marlon King had seen a penalty saved by David Marshall.
But Cardiff levelled with a goal from nothing as Mark Hudson fired in a cross from Peter Whittingham and Blues could not find a winner.
Birmingham boss Chris Hughton made four changes to his line-up, with Jordon Mutch, Wade Elliott, Huseklepp and Pablo Ibanez coming in.
The visitors named an unchanged side following their 2-2 draw at home to Coventry in midweek.
Cardiff started brightly but Joe Mason screwed a shot horribly wide while defender Hudson cleared the crossbar with a header.
Lifelong Birmingham fan Ben Turner thought he had opened the scoring on the quarter-hour when he found space in the box and tried to bend the ball around Boaz Myhill but his shot went inches wide.
A fluid counter-attack from Blues resulted in a corner which was not dealt with by Cardiff and when the ball fell to Guirane N'Daw he let fly from 30 yards but his shot was comfortably gathered by Marshall.
The Bluebirds were dominating as half-time approached and the lively Mason was close to converting a low cross from Don Cowie before the same player flashed a shot past the left post.
Birmingham had failed to impress in the first half but looked much better at the start of the second and they were handed a great chance to break the deadlock.
Chris Burke played the ball through to Mutch who was fouled in the area by Cowie. King stepped up to take the resulting penalty but his low effort was turned away by Marshall.
From their next attack, Blues found Huseklepp one-on-one with the keeper but Marshall saved well with his legs.
The opening goal did not take much longer to arrive, with Norwegian Huseklepp getting the better of Marshall from close range after a superb solo run from Burke on the break.
But, just as Birmingham looked set to go on and secure three points, Cardiff snatched an equaliser out of nothing.
Whittingham's cross fell to defender Hudson and he volleyed the ball into the bottom corner.
Blues were straight back on the attack, though, and only a great save from Marshall denied Burke as his shot on the turn looked destined for the top corner.
Cardiff responded through substitute Rudy Gestede but his right-foot volley from the edge of the box was straight at Myhill.
Marshall was almost embarrassed by a weak Burke shot which hit a bobble on the pitch and looped up but he clawed the ball away.
The Bluebirds almost stole the points at the death as Gestede came close with a header.