Vulnerability

A weakness in a system that an attacker can exploit to violate a security property, such as confidentiality, integrity, or availability.

Exploit: A method or code that takes advantage of a vulnerability to produce an unintended effect. It turns a weakness into an actionable attack.
Computer security: The practice of protecting computer systems and information from unauthorized access, damage, or disruption. Vulnerability is a central concern within this broader discipline.
Heartbleed: A 2014 vulnerability in OpenSSL's TLS heartbeat extension that allowed attackers to read process memory. It exposed sensitive data through a bounds-checking failure.
Zero-day vulnerability: A vulnerability unknown to the vendor or lacking an available fix when exploitation begins. It is a vulnerability whose defenders have little or no patching lead time.
Attack surface: The set of points where an attacker can attempt to enter or affect a system. Exposed interfaces determine where vulnerabilities can be reached.
Security property: A condition a system is designed to preserve, such as confidentiality, integrity, or availability. A vulnerability matters when exploitation can violate such a condition.
Shellshock: A family of vulnerabilities in GNU Bash that allowed command execution through crafted environment variables. It shows how a parser flaw can cross security boundaries.
Exploitability: The degree to which a vulnerability can be used to carry out an attack. A weakness may exist without being practically exploitable.
Threat modeling: A structured process for identifying threats, system weaknesses, and security mitigations. It helps locate vulnerabilities before attackers do.
Threat (computer security): A potential cause of an unwanted security incident that could harm a system or its information. Threats may exploit vulnerabilities to cause security incidents.

Linked from 6 pages