Burnett is a CIA agent.
Burnett was in the safehouse along with Vaughn, Weiss and Sydney after they abducted Jeroen Schiller. Burnett announced to Vaughn that they were in and told Sydney they had Kelvin give Sloane access to a fake website that had information about the Hensel Vaccine Inhaler to keep SD-6 occupied for months. In other words, the CIA had access to all of their accounts and contacts. Burnett then said the whole play was Vaughn's idea, much to Sydney's surprise.