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Container Image Scanning: A Complete Guide to Securing Your Containers

Container images bundle your application code with an entire OS filesystem, system libraries, and runtime dependencies. A single image can contain hundreds of packages — each with its own vulnerability history. Container image scanning analyzes every layer to find what is vulnerable, misconfigured, or malicious before the container reaches production.

18 min readUpdated May 2026

What Is Container Image Scanning?

Container image scanning is the automated process of analyzing the contents of a container image — layer by layer — to identify security vulnerabilities, malware, hardcoded secrets, misconfigurations, and license compliance issues. Scanners decompose each image layer, catalog every installed package (both OS and application), match them against vulnerability databases, and generate a Software Bill of Materials (SBOM).

Scanning should happen at multiple points: when the image is built in CI, when it is pushed to a container registry, and continuously in the registry as new CVEs are published. Admission controllers in Kubernetes can enforce that only scanned, policy-compliant images are allowed to run.

What Container Scanners Detect

OS Package CVEs

Known vulnerabilities in OS packages like openssl, glibc, curl, and zlib. The most common finding category — a typical base image has 50–200 CVEs.

App Dependency Vulns

Vulnerabilities in language-specific packages (npm, pip, Maven, Go modules) installed inside the image.

Malware & Trojans

Cryptominers, backdoors, and trojanized binaries embedded in image layers. Detected via ClamAV and YARA signature matching.

Secrets in Layers

API keys, passwords, private keys, and tokens accidentally baked into image layers during build. Even deleted files persist in earlier layers.

Misconfigurations

Running as root, exposed sensitive ports, missing HEALTHCHECK, using latest tag, and missing USER directive in Dockerfile.

Outdated Base Images

Base images older than 90 days or using deprecated versions (node:10, python:2.7, centos:6) that no longer receive security patches.

How Container Scanning Works

1

Layer Decomposition

The scanner pulls and unpacks the image, analyzing each layer independently. This reveals files added, modified, or deleted at each build step.

2

Package Cataloging

OS packages (dpkg, rpm, apk) and language packages (package.json, requirements.txt, go.sum, pom.xml) are inventoried to build a complete SBOM.

3

Vulnerability Matching

Each package is matched against vulnerability databases — NVD, OSV, GitHub Advisory, Alpine SecDB, Debian Security Tracker, and vendor-specific databases.

4

Policy Evaluation

Findings are evaluated against organizational policies: CVSS thresholds, blocklisted packages, required base images, and compliance framework requirements.

Container Security Best Practices

Build Phase

Use minimal base images (distroless, Alpine, slim variants)
Pin base image digests, not tags — tags are mutable
Add USER directive — never run as root
Include HEALTHCHECK instruction
Use multi-stage builds to exclude build tools
Clean up package manager caches in the same layer

Deploy Phase

Scan images in CI — fail builds for critical CVEs
Re-scan images in registry continuously for new CVEs
Use admission controllers to block unscanned images
Generate and store SBOMs with each image version
Enforce image signing with Cosign or Notation
Set resource limits and read-only root filesystem

Scan Container Images with TigerGate

TigerGate scans container images for vulnerabilities, malware, secrets, and misconfigurations — then monitors running containers with eBPF for runtime anomaly detection.

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