Security bug

A security bug or security defect is a software bug that can be exploited to gain unauthorized access or privileges on a computer system. Security bugs introduce security vulnerabilities by compromising one or more of:
 * Authentication of users and other entities
 * Authorization of access rights and privileges
 * Data confidentiality
 * Data integrity

Security bugs do not need be identified nor exploited to be qualified as such and are assumed to be much more common than known vulnerabilities in almost any system.

Causes
Security bugs, like all other software bugs, stem from root causes that can generally be traced to either absent or inadequate:
 * Software developer training
 * Use case analysis
 * Software engineering methodology
 * Quality assurance testing
 * and other best practices

Taxonomy
Security bugs generally fall into a fairly small number of broad categories that include:
 * Memory safety (e.g. buffer overflow and dangling pointer bugs)
 * Race condition
 * Secure input and output handling
 * Faulty use of an API
 * Improper use case handling
 * Improper exception handling
 * Resource leaks, often but not always due to improper exception handling
 * Preprocessing input strings before they are checked for being acceptable

Mitigation
See software security assurance.