"Our efforts have not reduced the group’s terrorism capability and global reach."
The four officers died in the line of duty in Africa, Asia and Iran.
Three Senate Democrats are asking Obama to get involved.
"Heroizing such individuals I find to be unfathomable," John Brennan said.
The Senate is expected to easily pass cyber legislation later on Tuesday.
The initial emails posted by the anti-secrecy organization date from 2007 and 2008.
A group of Senate Democrats had demanded John Brennan revise comments from March.
"They’re looking for the seams to operate within,” John Brennan said.
“In our judgment your handling of this matter has undermined that confidence."
John Brennan's comments come in the final weeks of negotiations over Iran's nuclear program.
John Brennan warned about a new generation of terrorists spreading their message online.
CIA chief praised selection of Avril Haines as the president's deputy national security adviser.
Brennan previously said it would be a mistake to release the pages because of inaccuracies.
John Brennan's appearance was stalled for long stretches as protesters chanted.
The reported teenager claims to have hacked James Clapper and his wife.
CIA Director John Brennan said Monday that the Islamic State in Iraq and Syria (ISIS) may have more...
Media outlets made inappropriate "inferences" about the hack, John Brennan said.
The classified documents date from the Kennedy and Johnson administrations.
The visit comes ahead of a key deadline at the end of the month.
The Saudis are taking Hezbollah's expansion of regional practice and operations seriously.
His campaign offers the possibility that a debate about the use of drones will reemerge.
However, "there’s an alignment of some interest," according to the head of the CIA.
The spy agency is making its biggest changes in years.
“To say that it’s unknowable, I would disagree with that,” Rep. Mike Rogers said.