Container scanning inspects images and their configuration before deployment to find known vulnerabilities, secrets and bad settings. Runtime protection watches containers while they run and reacts to behavior. They overlap a little and catch different problems, so most teams start with scanning and add runtime controls where risk justifies it.
What does each one look at?
NIST SP 800-190, the Application Container Security Guide, explains the security concerns of containers and gives recommendations. It discusses risks across the image, the registry, the orchestrator, the containers themselves and the host operating system.
Scanning works on the first of these. It reads an image, lists the packages and layers inside, compares them to vulnerability data and checks for things such as embedded credentials or a root user. It runs at build time, in the registry and sometimes on a schedule against images already deployed.
Runtime protection works on the live system. It observes processes, network connections and file access in running containers, and applies policies such as blocking an unexpected shell or an outbound connection to a new address.
Where do they overlap?
Both can flag a container running as root, and both can tell you a known bad package is present, if the runtime tool inspects what is loaded. The overlap is narrow. The tools answer different questions.
Scanning asks: what is in this image, and is it known to be risky? Runtime asks: what is this container doing right now, and is it normal?
What does scanning miss?
A scan cannot see a flaw nobody has published yet. It cannot see a misuse of a legitimate tool, such as a stolen credential used from inside a container. It also cannot tell you whether the vulnerable function in a package is ever called, unless paired with reachability analysis.
What does runtime protection miss?
It reacts after the container starts. By the time a runtime rule fires, the vulnerable image is already in production. It also requires tuning, because a policy that alerts on normal behavior trains people to ignore it. And it is blind to risks that never show as unusual behavior, such as a library with a license problem.
A constructed example
Constructed example: a team ships an image with an old XML parsing library that has a published flaw. Scanning at build flags it and the team updates the dependency. Months later, an attacker gets a stolen token and runs commands in a pod. No package is vulnerable here, so the scan stays quiet. A runtime rule that flags an unexpected shell inside an application container catches it. Each tool covers the other's gap.
How should you decide?
Start from your risks.
- If your main exposure is shipping known vulnerable components, begin with scanning in the pipeline and a policy to block on severity or reachability.
- If you hold sensitive workloads or face targeted attackers, add runtime detection for the highest value services.
- If you have neither a scan gate nor an inventory, do not start with runtime. You will alert on noise from images you do not understand.
Order matters because scanning is cheap, deterministic and easy to explain, while runtime needs ownership and response.
For the scanning side, Safeguard offers SBOM generation, dependency scanning and reachability analysis, and the free browser scan at gold.safeguard.sh/scan covers up to 100 dependencies. Safeguard does not provide runtime protection tooling, so evaluate that category separately.
Open the dependency inventory demo
What to do
- Generate an SBOM for each image at build time and store it with the image.
- Scan on build and again on a schedule for images already deployed.
- Set a gate: block new critical issues that are reachable, track the rest.
- Run containers as non root with minimal images and read only file systems where possible.
- Pick two or three critical services for runtime monitoring and write the response steps first.
- Review alerts monthly and tune or remove noisy rules.
Quick check
Can runtime protection replace image scanning?
No. Runtime tools react to behavior after deployment, while scanning prevents known issues from shipping. They answer different questions.
Which should a small team add first?
Usually scanning, because it is cheap and acts before deployment. Add runtime monitoring for high value services once you have inventory and response steps.
Sources
Last reviewed: 18 October 2026.
