IBM System Z Mainframes are in regular use in Fortune 500 companies. Far from being legacy these systems are running an actively maintained operating system (z/OS). Applications on these often occupy roles critical to the business processes they underpin- with much of the later technology built around them- rather than replacing them. However- these systems are often bypassed by security testing due to worried of availability or assumptions about legacy.This talk will introduce you to assessing mainframe applications- which turn out to be quite similar to web applications. For this purpose we built a tool- Big Iron Recon & Pwnage (BIRP)- to assist with performing such assessments.Importantly- our research uncovered a family of mainframe application vulnerabilities introduced by the TN3270 protocol. We found numerous applications- but not all- vulnerable to these flaws. Applications running within the two most popular transaction managers (CICS and IMS) as well as one of IBM’s own applications. The tool released assists with the exploitation of these flaws.