The set of ways in which an adversary can enter a system and potentially cause damage.
Extended Definition: An information system’s characteristics that permit an adversary to probe, attack, or maintain presence in the information system.
Adapted from: Manadhata, P.K., & Wing, J.M. in Attack Surface Measurement, retrieved from http://www.cs.cmu.edu/~pratyus/as.html#introduction
Source: NICCS™ Portal Cybersecurity Lexicon, National Initiative for Cybersecurity Careers and Studies (https://niccs.us-cert.gov/glossary) as of 11 November 2015, Global Standards