Key Takeaways
- Container image scanning detects known vulnerabilities in packages, libraries, dependencies, and other components before they reach production.
- Scan images throughout the lifecycle, from development and CI/CD builds to registries and production monitoring, to catch newly disclosed vulnerabilities.
- SBOMs help you identify the software components inside an image and connect them to known vulnerabilities.
- Minimal, hardened, and distroless images reduce unnecessary components and attack surface, but they still require vulnerability scanning.
- A scan is only the first step. Assess, remediate, rebuild, rescan, and verify each finding before deploying the image.
What Is Container Image Scanning?
Container image scanning checks the software inside a container image for known vulnerabilities. It analyses image layers, operating system packages, libraries, and application dependencies to identify components that may introduce security risks before deployment.
Container image scanning is one of the core operational capabilities of Image Security. Users should first understand why container images must be protected before learning how scanning continuously validates their security posture.
Why Is Container Image Scanning Important?
Container image scanning helps identify vulnerabilities before vulnerable software reaches production. It:
- Detects known vulnerabilities in base images, operating system packages, libraries, and application dependencies.
- Identifies inherited vulnerabilities that enter an image through its base image and dependencies.
- Gives security teams visibility into vulnerable components before deployment.
- Helps teams prioritise findings based on severity, exploitability, and business impact.
- Supports remediation by identifying packages that need updates, replacement, or removal.
- Enables continuous validation as new vulnerabilities and CVEs emerge after an image is built.
Vulnerabilities present in Base Images propagate into every derived container image. Scanning trusted base images early helps eliminate inherited security risks throughout the container lifecycle.
What Does Container Image Scanning Detect?
Container image scanning identifies known security issues in the software components packaged inside an image. It examines image layers, operating system packages, libraries, and application dependencies to find vulnerable components before deployment.
It can detect:
- Vulnerable packages: Identifies operating system packages and libraries with known security vulnerabilities.
- Application dependency risks: Finds vulnerabilities in third-party libraries and dependencies included in the image.
- Known CVEs: Matches software components against vulnerability databases to identify publicly disclosed CVEs.
- Affected components: Shows which packages or dependencies contain identified vulnerabilities, making remediation more targeted.
- Severity information: Reports vulnerability severity so security teams can assess findings and prioritize remediation.
Container image scanning performs vulnerability detection by identifying known weaknesses within image components. This relationship connects the discovery process with the broader vulnerability management lifecycle.
How Does Container Image Scanning Work?
Container image scanning identifies the software components inside an image and matches them against vulnerability databases and security advisories. It then reports affected packages and dependencies so security teams can assess the findings and determine the appropriate remediation.
The process typically includes:
- Identify the image: Select the image and version to scan.
- Inspect image contents: Analyse image layers, operating system packages, libraries, and application dependencies.
- Identify components: Determine the software packages and versions present in the image.
- Match vulnerabilities: Compare identified components with vulnerability databases and security advisories.
- Report findings: Show affected components, CVEs, and available severity information.
- Validate remediation: Rebuild the image after fixing identified issues and scan it again to verify the changes.
Many image scanners leverage SBOMs to identify vulnerable software components more accurately and efficiently. This relationship connects software inventory with automated vulnerability analysis.
When Should You Scan Container Images?
Scan container images during development, CI/CD builds, before deployment, and when new vulnerabilities are disclosed. Scanning at these points helps you catch vulnerable components before production and reassess images when new risks emerge.
- During development: Scan early to identify vulnerable packages and dependencies before they move into later stages of the delivery process.
- During image builds: Image scanning is commonly integrated into secure build pipelines to prevent vulnerable images from progressing through CI/CD workflows. This relationship embeds security validation directly into software delivery.
- Before deployment: Scan the final image to validate the exact artifact that will run in production.
- After new CVEs are disclosed: Rescan existing images to determine whether newly reported vulnerabilities affect deployed components.
DevSecOps pipelines automate container image scanning during software development and deployment. This relationship demonstrates how continuous security validation becomes part of modern software engineering practices.
How Does Image Scanning Support Vulnerability Management?
Container image scanning identifies vulnerabilities in image components. Vulnerability management helps teams assess, prioritize, and remediate those findings based on their severity, exploitability, and impact.
The workflow is straightforward:
- Detect: Identify vulnerable packages, libraries, and dependencies inside container images.
- Assess: Evaluate each finding based on severity, exploitability, and business impact.
- Prioritize: Focus remediation on vulnerabilities that pose the greatest risk.
- Remediate: Update packages, replace vulnerable dependencies, or rebuild affected images.
- Verify: Rescan rebuilt images to confirm that fixes address the identified vulnerabilities.
Image scanning identifies vulnerabilities within container images. Vulnerability management then assesses, prioritizes, and remediates those findings by updating packages, replacing vulnerable dependencies, or rebuilding affected images. Image scanning also identifies publicly disclosed CVEs affecting software packages within container images. CVE management tracks, prioritizes, and resolves these findings over time.
Reducing container image risk starts with controlling vulnerable components before deployment, not just scanning them afterward. CleanStart helps you understand image contents, dependencies, and inherited risk so you can reduce vulnerabilities at the image layer before they reach production.
How Do Minimal, Hardened, and Distroless Images Affect Scanning?
Minimal, hardened, and distroless images still require vulnerability scanning. They reduce the number of packages and components in an image, but they do not eliminate vulnerabilities.
Why Do Smaller Images Still Need Scanning?
Minimal images remove unnecessary packages, tools, and libraries. This reduces the attack surface and leaves fewer components that can contain known vulnerabilities. However, the components that remain can still have CVEs. Application libraries, runtime dependencies, and required packages may become vulnerable even after an image is minimized.
Minimal images reduce the number of components that need protection. Scanning verifies that those remaining components do not contain known vulnerabilities.
How Does Scanning Validate Hardened Images?
Hardened Container Images use security-focused configurations and remove unnecessary components. Scanning verifies whether those changes have reduced the image's known vulnerability exposure. A scan can still identify vulnerable packages or dependencies in a hardened image. Teams can then update, remove, or replace the affected components, rebuild the image, and scan it again.
Do Distroless Images Still Need Scanning?
Yes. Distroless Images remove most operating system utilities and other nonessential components, but they can still contain vulnerable application dependencies and runtime libraries. Scanning checks the components that remain and identifies known vulnerabilities before deployment. This makes scanning important even when an image has a very small software footprint.
The principle is straightforward: minimisation reduces the attack surface; scanning checks the remaining components for known vulnerabilities.
How Do Image Scanning and Image Signing Work Together?
Container image scanning checks an image for known vulnerabilities, while image signing verifies its authenticity and integrity. Teams should scan images before signing them so only validated artifacts receive trusted signatures.
What Does Image Scanning Validate?
Image scanning checks an image's layers, OS packages, libraries, and dependencies for known vulnerabilities. Teams assess the findings and decide whether the image meets their security requirements. If a scan finds a vulnerability that needs remediation, teams can update the affected component, rebuild the image, and scan it again before approval.
What Does Image Signing Verify?
Image signing confirms the authenticity and integrity of a container image. A digital signature helps confirm that the image came from a trusted source and has not been modified after signing. A valid signature does not prove that an image is secure. It verifies the image's authenticity and integrity, not its vulnerability status.
Why Should You Scan Before Signing?
Images should be scanned before they are digitally signed to ensure only validated artifacts receive trusted signatures. Together, scanning and signing establish both security and authenticity before deployment.
The workflow is:
Build → Scan → Assess → Remediate → Approve → Sign → Deploy
This process also applies to immutable images. Images should be scanned before they become immutable because changes cannot be made afterwards. If a vulnerability is discovered later, teams should rebuild and validate a new image instead of modifying the existing artefact.
Scanning and signing provide two separate controls: scanning identifies known security risks, while signing verifies the identity and integrity of the approved image.
How Does Image Scanning Strengthen Software Supply Chain Security?
Container image scanning identifies known vulnerabilities in base images, third-party packages, and application dependencies before you deploy them. It helps you catch software supply chain risks before they reach production.
How Do Base Images and Dependencies Introduce Risk?
Your container image can include software maintained outside your team. A vulnerable base image can pass that vulnerability into every image you build from it. Third-party libraries and dependencies can introduce similar risks. Scanning identifies these components and checks them against vulnerability databases. You can then update, replace, or remove affected components before deployment.
How Does Scanning Validate Software Artifacts?
Software Supply Chain Security requires you to understand what goes into your software artifacts and identify known risks before deployment. Container image scanning verifies that software artifacts entering the supply chain are free from known vulnerabilities. This helps you assess their security before they progress toward production.
You can add scanning to your CI/CD workflow and use security policies to block images that exceed your acceptable vulnerability thresholds. Scanning does not guarantee that an image is completely secure. It helps you detect known vulnerabilities early, so you can assess and address them before they affect production workloads.
How Does Continuous Image Scanning Improve Container Security?
Continuous image scanning finds new vulnerabilities in container images after the initial scan. You need it because new CVEs can affect an image even after it passes a pre-deployment security check.
Why Is One-Time Scanning Not Enough?
A one-time scan only captures vulnerabilities known at that point. Security researchers can disclose new CVEs days, weeks, or months later. Those vulnerabilities may affect images you already store or run. For example, an image can pass your CI/CD scan today. A new CVE may later affect one of its libraries. Without another scan, you may not know that the image needs remediation.
How Does Continuous Scanning Work?
You can rescan images on a schedule or trigger scans when vulnerability databases add new findings. When a scan identifies a new vulnerability, you can locate the affected component, assess the risk, and rebuild the image if necessary. Continuous scanning also helps you track older images that remain in use. Prioritise findings based on factors such as severity, exploitability, and whether the affected image is deployed.
How Does Image Scanning Relate to Runtime Security?
Image scanning reduces known vulnerabilities before deployment. Runtime security protects workloads while they run. You need both controls because securing the image does not protect against every runtime threat. Scanning helps you address known weaknesses in the image. Runtime controls help detect and respond to threats that emerge after deployment.
How Does Container Image Scanning Support Compliance?
Container image scanning helps you enforce vulnerability policies before deployment and maintain records of security checks. It shows which images you scanned, what vulnerabilities you found, and how you addressed them.
What Role Does Scanning Play in Compliance?
Security and compliance programs often require organisations to identify and address software vulnerabilities before deployment. Scanning lets you check container images against defined vulnerability thresholds. You can set policies that block images with critical or high-severity vulnerabilities. This creates a consistent security gate in your CI/CD pipeline.
How Does Scanning Help With Auditability?
Container security compliance requires evidence of your security controls. Scan reports can record the image version, scan date, detected vulnerabilities, severity levels, and remediation status. You can combine these records with SBOMs, remediation reports, and deployment policies to support audits and demonstrate that your vulnerability controls are working.
What Are the Limitations of Container Image Scanning?
Container image scanning detects known vulnerabilities in image components, but it cannot identify every security risk. You still need vulnerability assessment, remediation, and runtime controls to address issues beyond scan coverage.
1. What Can Image Scanning Miss?
Scanners compare image components with vulnerability databases. They can detect known CVEs in supported packages and dependencies, but they cannot reliably identify every security flaw.
Image scanning may miss:
- Zero-day vulnerabilities
- Application logic flaws
- Runtime attacks
- Malicious behavior
- Issues outside the scanner's detection scope
A clean scan means the scanner found no known vulnerabilities within its coverage. It does not prove that the image is risk-free.
2. Why Can Different Scanners Report Different Results?
Different scanners use different vulnerability databases, package mappings, detection methods, and update schedules. They can therefore produce different results for the same image. You should check the scanner's database coverage and package detection methods when comparing results.
3. Why Do Scan Results Need Review?
A scanner's severity rating does not always reflect the actual risk to your application. You need to check whether the affected component exists, whether your application uses it, and whether an attacker can exploit the vulnerability. A vulnerability assessment adds this context. It helps you determine which findings need immediate remediation and which require further review.
4. Why Is Remediation Still Necessary?
A scan only identifies the problem. You still need to update, replace, remove, or rebuild affected components. After remediation, rescan the image to confirm that the vulnerability no longer exists.
5. Why Is Image Scanning Only One Security Control?
Image scanning focuses on vulnerabilities inside container images. It does not replace secure coding, dependency management, access controls, image hardening, or runtime security.
Use scanning alongside these controls to protect the container across its lifecycle.
How Should You Act on Container Image Scan Results?
Act on scan results by identifying the affected component, assessing its risk, applying the right fix, and rescanning the image. This turns a scan report into a clear Vulnerability Remediation workflow.
Here’s how you should handle container image scan results:
- Identify the Affected Component: Check the package, library, or dependency linked to the finding. Review its version, image layer, CVE, and available fixed version.
- Assess Severity and Exploitability: Review the CVE severity, exploit availability, application usage, and exposure. A critical CVE may not pose the same risk in every environment.
- Choose the Right Remediation: Update the vulnerable package, replace the dependency, remove an unnecessary component, or switch to a safer base image. If the vulnerability comes from a base image, update the base image and rebuild the affected images.
- Rebuild the Image: Create a new image after applying the fix. Do not modify an existing production artifact in place.
- Rescan After Remediation: Scan the rebuilt image to confirm that the vulnerability is resolved. Check for new findings introduced during the rebuild.
- Track the Fix: Record the affected image, vulnerability, remediation action, and verification result. This supports ongoing CVE management and gives your team a clear record of how each finding was handled.
Improving Container Image Security with CleanStart
CleanStart helps you reduce vulnerabilities in container images with hardened images, trusted libraries, SBOMs, and software supply chain visibility. These capabilities help you identify vulnerable components, reduce inherited risk, and make better security decisions before deployment.
This is how CleanStart supports container image security:
- Hardened Container Images: CleanStart provides hardened container images with minimal foundations and near-zero CVEs. Starting with these images can reduce the vulnerabilities you inherit before you build your application image.
- SBOM and Dependency Insight: CleanStart automatically generates SPDX 3.0 SBOMs during image builds. The SBOM documents packages, libraries, dependencies, and versions, helping you identify the components that require vulnerability assessment.
- Vulnerability Visibility: CleanSight continuously identifies inherited software supply chain risks across container environments. You can see affected images, packages, and vulnerabilities and prioritize remediation accordingly.
- Verified Image Provenance: CleanStart provides signed provenance and SBOMs for its images. You can verify the image's origin, build information, and software components before deployment.
- Inherited Risk Reduction: CleanStart's hardened images help you reduce vulnerabilities at the base-image layer. This means fewer known vulnerabilities can flow into the application images you build from them.
Book a demo with CleanStart to see how you can reduce inherited vulnerabilities and strengthen container image security before deployment.
