Zerologon

What Is an Exploit: How a Flaw in Someone Else's Code Becomes Unauthorized Access to Your Server

The article explains the critical distinction between a vulnerability and an exploit using the Log4Shell incident as the primary example. It breaks down how Log4j's JNDI lookup flaw allowed remote code execution simply by logging a crafted string, leading to CVE-2021-44228 with a maximum CVSS score. The piece covers the full lifecycle from vulnerability discovery to payload delivery, including memory corruption, injection flaws, and logical errors. It details defensive mechanisms such as stack canaries, DEP, ASLR, and CFG, along with attacker responses like ROP chains. Real-world cases including Zerologon, Heartbleed, Stuxnet, and WannaCry illustrate the progression from single bugs to multi-stage exploit chains. The text also addresses zero-day economics, exploit kits, bug bounty programs, and practical mitigation strategies centered on KEV catalogs and EPSS scoring.