"I don't know how often we are going to leave the door open at the back, a bit of fear has crept in there somehow," said the Bluebirds manager.
"At the moment that unit isn't working. We are the second biggest scorers so there is nothing wrong going forward.
"If you don't score you have to keep a clean sheet and that isn't happening."
Cardiff still lie second in the table, just four points behind Championship leaders QPR.
Boro loss frustrates Cardiff
That is despite a terrible November where they took just four points from a potential 15.
In their first game in December they needed a last-minute equaliser from substitute Andy Keogh to secure a home draw with bottom-side Preston.
And on Saturday Julio Arca's first league goal for three years saw the Bluebirds defeated at relegation battlers Boro.
"Too often we end up chasing the game," said a frustrated Jones.
"I wouldn't mind if we were beaten by good movement but it was a punt down the middle and a sloppily conceded penalty and that shouldn't happen.
"We have to make sure we don't get carried away and let a blame culture creep in but right now they need a bit of criticism. It is harsh but they have to accept it."
Source: BBC Sport
Source: BBC Sport