Dockerfiles are the backbone of modern DevOps workflows. They define how we build, package, and deploy software in the cloud and across CI/CD pipelines. But what’s often overlooked is that every line in your Dockerfile represents a potential supply chain risk. In 2025, attackers are increasingly targeting dev containers — not your code — as the initial point of compromise.
This article walks through how Dockerfiles can become liabilities, real-world attacks that have occurred due to insecure container practices, and what you can do to protect your pipeline from becoming a staging ground for the next breach.
The Hidden Risk in Every Dockerfile
A Dockerfile may seem simple, but it’s essentially a blueprint that defines your entire runtime environment. Here’s what’s often included:
- A base image like Ubuntu, Alpine, or Node
- A list of packages and system tools
- Package manager operations like installing dependencies
- Environment variables and file copies
- Occasionally, secrets or tokens accidentally hardcoded
All of this can introduce vulnerabilities if not properly controlled.
Insecure Base Images
Using common tags like latest might seem convenient, but it's a dangerous shortcut:
- You don’t control what gets pulled
- There’s no guarantee it’s free of vulnerabilities
- It can change under your feet and introduce bugs or backdoors
Even official base images have had vulnerabilities. In several cases, malware-laden images were mistakenly trusted simply because they looked "official." Using minimal or distroless images reduces attack surface, but only if you verify their integrity.
Dependency Poisoning
When your Dockerfile installs dependencies without strict version control or validation, you expose your build to upstream attacks. Examples include:
- Pulling unverified packages from PyPI, npm, or other registries
- Failing to use lockfiles or hashes
- Installing dependencies with known CVEs
Malicious actors often upload lookalike packages or compromise rarely maintained ones to spread malware downstream.
Secrets in Build Context
It’s shockingly common for developers to copy .env files or credentials into containers during the build. Even if these are removed later in the build, they may persist in intermediate layers or cached metadata.
This results in image history containing secrets, which can then be extracted by attackers from public container registries or leaked backups.
Public Registry Abuse
Docker Hub and similar registries are targets for impersonation attacks. Anyone can upload an image named to mimic a legitimate one. This has led to incidents where:
- Developers unknowingly pulled malicious images due to typos
- Organizations trusted compromised community images
- Attackers used container startup scripts to exfiltrate secrets or mine crypto
Pulling from unverified or unofficial registries opens up a massive trust issue. Without signed and verified images, you’re vulnerable every time your pipeline runs.
Sign and Verify Images with cosign
After building your image, you can sign it like this:
# Generate a key pair
cosign generate-key-pair
# Sign the image
cosign sign --key cosign.key docker.io/youruser/yourimage:tag
To verify the image before deployment:
cosign verify --key cosign.pub docker.io/youruser/yourimage:tag
Why it’s secure:
- Adds cryptographic integrity to your container
- Prevents tampering between CI and deployment
- Required by many supply chain security frameworks (e.g., SLSA)
Defense Strategies That Actually Work
Image Signing
Use tools like Cosign to sign and verify container images before use. This ensures that you only run images your team has verified or built internally.
SLSA Compliance
Supply-chain Levels for Software Artifacts (SLSA) is a framework for ensuring that software is built from known sources, by secure processes. Adopting even SLSA Level 1 can prevent most tampering and misconfiguration in your container builds.
Use Distroless Images
Distroless images strip out unnecessary package managers and shells, reducing the surface area for attack. They also prevent you from accidentally adding tools or secrets during later stages.
Using a Distroless Image with Multi-Stage Builds
This reduces attack surface and ensures secrets don’t persist in the final image:
# Stage 1: Build the app
FROM golang:1.20 AS builder
WORKDIR /app
COPY . .
RUN go build -o app
# Stage 2: Create minimal runtime image
FROM gcr.io/distroless/static:nonroot
COPY --from=builder /app/app /
USER nonroot:nonroot
ENTRYPOINT ["/app"]
Why it’s secure:
- Uses a trusted base (distroless)
- Eliminates shell and package managers from final image
- No root user
- Secrets never copied into runtime container
CI/CD Pipeline Controls
Harden your pipelines:
- Disallow
latesttags - Scan every container with tools like Trivy or Grype
- Validate SBOMs before shipping
- Require peer review for Dockerfile changes
Final Thoughts
Dockerfiles are not just instructions. They are part of your application’s trusted computing base. Treat them like infrastructure-as-code — auditable, locked-down, and verified. Your CI pipeline, production environment, and customer data depend on it.
Ignoring the security of your containers in 2025 is like shipping software without passwords in 2005. There’s no excuse anymore. Secure your Dockerfiles now or risk becoming the next cautionary tale in a breach report.
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