Traditional container security relied on periodic image scanning and manual patching. This approach was designed for a slower development environment where applications were updated infrequently and the open source footprint was relatively small. Modern applications are built almost entirely on open source, with AI coding assistants accelerating the rate at which new dependencies are introduced. A static approach — build the image, scan it, patch what the scanner finds — generates a growing backlog of unresolved vulnerabilities as new CVEs are continuously disclosed against components already in production.

Reactive container security starts with what is already in the environment and tries to reduce the vulnerability count through patching. Proactive container security starts before any component enters the image — governing what open source can be included, building from verified source with signed attestations, and automating continuous monitoring and remediation under contractual SLAs. The practical difference is that proactive teams start from near-zero CVEs at build time and maintain that posture through automated rebuilds, while reactive teams start from whatever the public registry provides and work backward from scanner findings.

A container image that passes scanning at build time begins accumulating new CVE exposure the moment new vulnerabilities are disclosed against its components. Nightly rebuilds ensure that patched versions of affected components are incorporated automatically rather than waiting for a manual update cycle. VEX — Vulnerability Exploitability eXchange — advisories provide machine-readable documentation of which CVEs in a container are actually exploitable given its specific build configuration, allowing scanners to filter false positives. Together, nightly rebuilds and VEX advisories convert the container security posture from a point-in-time measurement into a continuously maintained standard.