  Command, Control, Communication, and Intelligence (C3I) systems are
increasingly used in critical civil and military domains for achieving
information superiority, operational efficacy, and greater situational
awareness. Unlike traditional systems facing widespread cyber-attacks, the
sensitive nature of C3I tactical operations make their cybersecurity a critical
concern. For instance, tampering or intercepting confidential information in
military battlefields not only damages C3I operations, but also causes
irreversible consequences such as loss of human lives and mission failures.
Therefore, C3I systems have become a focal point for cyber adversaries.
Moreover, technological advancements and modernization of C3I systems have
significantly increased the potential risk of cyber-attacks on C3I systems.
Consequently, cyber adversaries leverage highly sophisticated attack vectors to
exploit security vulnerabilities in C3I systems. Despite the burgeoning
significance of cybersecurity for C3I systems, the existing literature lacks a
comprehensive review to systematize the body of knowledge on C3I systems'
security. Therefore, in this paper, we have gathered, analyzed, and synthesized
the state-of-the-art on the cybersecurity of C3I systems. In particular, this
paper has identified security vulnerabilities, attack vectors, and
countermeasures/defenses for C3I systems. Furthermore, our survey has enabled
us to: (i) propose a taxonomy for security vulnerabilities, attack vectors and
countermeasures; (ii) interrelate attack vectors with security vulnerabilities
and countermeasures; and (iii) propose future research directions for advancing
the state-of-the-art on the cybersecurity of C3I systems.
