Example embodiments relate to a network-based vulnerability detection system configured to access a database of customer transaction data corresponding to a set of card readers that includes transaction codes, receive an identification of a set of compromised card readers among the set of card readers, identify common transaction codes within the transaction data of the set of compromised card readers, and correlate the common transaction codes to one or more instances of fraud associated with the compromised set of card readers. In some example embodiments, the vulnerability detection system may be applied to monitor one or more card readers, receive transaction data corresponding to transaction conducted through the card readers, identify the common transaction codes correlated to the instances of fraud, and cause display of a notification that includes an indication of the instance of fraud at a client device.