A vulnerability chain is two or more flaws used together so that each one helps the attacker reach the next stage. One bug may bypass authentication, reveal sensitive data, or weaken a control; another may then turn that foothold into code execution, privilege escalation, or broader access. On their own, the flaws may look low impact, but combined they can become a serious break-in path.
Vulnerability chains matter because defenders must stop every link, not just the final one. Attackers often use them against web apps, servers, and enterprise platforms where different components interact. In practice, a proof-of-concept for one step can raise risk if a second weakness is already present. Good defenses include fast patching, reducing exposure, hardening configurations, and testing whether multiple bugs can be chained before attackers do.