Bug: Container Runs as Root User in Dockerfile

[Reactivity512]

Location:
ozontech/file.d/blob/master/build/package/Dockerfile
ozontech/file.d/blob/master/build/package/Dockerfile.scratch
ozontech/file.d/blob/master/build/package/Dockerfile_dev
ozontech/file.d/blob/master/build/package/Dockerfile_playground

Description:
All four Dockerfiles lack the USER instruction, causing the container to run as root (UID 0) by default. This violates the principle of least privilege (CWE-250). Even if a non-root user was created in previous build stages, it is not carried over to the final image; the USER instruction must be explicitly defined in the runtime stage.

Risk:

• If any vulnerability leading to code execution is exploited (RCE, SSRF with command execution capabilities, writeable path traversal, etc.), an attacker gains full control over the container.
• Root access within the container often allows an attacker to:
  • Install additional packages or malware,
  • Modify the host filesystem (if sensitive directories are mounted),
  • Bypass security restrictions in orchestrators (e.g., Kubernetes PodSecurityPolicies / Pod Security Admission).
• Direct violation of security standards and benchmarks:
  • CIS Docker Benchmark 4.1,
  • OWASP Docker Security,
  • Kubernetes Pod Security Standards (Restricted profile).

Screenshot

Empty value - run as root

Recommendations:

Add user creation and switch to the non-root user in the final stage of each Dockerfile:

# Example for Alpine-based images
RUN addgroup -S appgroup && adduser -S appuser -G appgroup
USER appuser

For the scratch-based image:

ARG APP_IMAGE=ubuntu:latest

# Build
FROM --platform=$BUILDPLATFORM golang:1.25-alpine AS build

RUN addgroup -S appgroup && adduser -S appuser -G appgroup

ARG VERSION
ARG BUILD_TIME
ARG TARGETARCH

WORKDIR /file.d

COPY go.mod go.sum ./

RUN go mod download

COPY . .

ENV CGO_ENABLED 0
ENV GOOS linux
ENV GOARCH ${TARGETARCH:-amd64}

RUN go build -trimpath \
    -pgo default.pgo \
    -ldflags "-X github.com/ozontech/file.d/buildinfo.Version=${VERSION}" \
    -o file.d ./cmd/file.d

# Deploy
FROM scratch

COPY --from=build /etc/passwd /etc/passwd
COPY --from=build /etc/group /etc/group
USER appuser

WORKDIR /file.d

COPY --from=build /file.d/file.d /file.d/file.d

CMD [ "./file.d" ]

In Kubernetes manifests, enforce this by adding the securityContext:

securityContext:
  runAsNonRoot: true
  runAsUser: 1001