Dictionary defines: vulnerability – open to attack, harm, or damage
CIS RAM defines: vulnerability – A weakness that could permit a threat to compromise the security of information assets.
Not simple.
ISO/IEC 27000 defines: vulnerability – weakness of an asset or control that can be exploited by one or more threats
Not simple
PCI DSS defines: vulnerability – Flaw or weakness which, if exploited, may result in an intentional or unintentional compromise of a system.
Not simple
CNSS defines: vulnerability – Weakness in an information system, system security procedures, internal controls, or implementation that could be exploited.
Not simple and relies on specialized terms
O-TTPS defines: Vulnerability – A weakness in the design, implementation, or operation of an asset, artifact, system, or network that can be exploited.
Not simple and relies on specialized terms
CVE defines a vulnerability – A weakness in the computational logic (e.g., code) found in software and hardware components that, when exploited, results in a negative impact to confidentiality, integrity, or availability.
Not simple and relies on specialized terms
EAS defines: vulnerability – A weakness in system security procedures, design, implementation, internal controls, etc. that could be accidentally triggered or intentionally exploited and could result in a violation of the system’s security policy
Not simple and relies on specialized terms
ISACA defines: vulnerability – A weakness in the design, implementation, operation or internal control of a process that could expose the system to adverse threats from threat events
Not simple and relies on specialized terms
NIST 800-53 defines: vulnerability – Weakness in an information system, system security procedures, internal controls, or implementation that could be exploited or triggered by a threat source.
Not simple and relies on specialized terms
OWASP describes: vulnerability – a hole or a weakness in the application, which can be a design flaw or an implementation bug, that allows an attacker to cause harm to the stakeholders of an application.
Not simple and relies on specialized terms
STIX defines: vulnerability – a mistake in software that can be directly used by a hacker to gain access to a system or network
Not simple and relies on specialized terms
FAIR defines: vulnerability – The probability that a threat event will become a loss event (which occurs when a threat agent acts against an asset)
Describes how to measure vulnerability rather than defining what it is.
SDL defines: threat – an attacker’s objective
This definition is related to definitions of vulnerability rather than threat, assuming the reader understand that “objective” refers to the vulnerability the attacker seeks to exploit.