Shift-left security: integrating Trivy and Semgrep in GitLab CI

Mon, 16 Mar 2026 00:00:00 +0000

Why these two tools and not others

The security tooling landscape for pipelines is huge, and it is easy to end up with a pipeline that spends twenty minutes just on scans. After trying several combinations, I stick with Trivy and Semgrep for a simple reason: they cover two distinct attack surfaces with minimal friction.

Semgrep analyzes your source code looking for dangerous patterns — SQL injections, insecure deserialization, hardcoded secrets. It does this fast and without needing to compile anything. Trivy, on the other hand, takes care of everything that is not your code: dependencies with known CVEs, outdated base images, problematic IaC configurations. Between the two you cover your own code and third-party code.

Both are open-source, run without an external server, and produce JSON output that you can easily parse in CI. No licenses or third-party dashboards needed to get started.

Pipeline structure

The idea is that security should not be an isolated stage at the end, but something that runs in parallel with the rest of your checks. Here is the general layout:

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stages:
 - test
 - security
 - build
 - deploy

variables:
 TRIVY_SEVERITY: "HIGH,CRITICAL"
 SEMGREP_RULES: "p/owasp-top-ten p/security-audit"

The security stage runs at the same level as test. If any scan fails, the pipeline stops before building the image or deploying anything.

Setting up Semgrep

Basic job

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semgrep:
 stage: security
 image: semgrep/semgrep:latest
 script:
 - semgrep ci --config "$SEMGREP_RULES" --json --output semgrep-results.json
 artifacts:
 paths:
 - semgrep-results.json
 when: always
 rules:
 - if: $CI_PIPELINE_SOURCE == "merge_request_event"
 - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH

This runs Semgrep on every merge request and on every push to the main branch. Results are always saved as an artifact, even if the pipeline fails — you will want to review them later.

Custom rules

Generic rulesets are fine to start with, but as soon as you have project-specific patterns you want to catch, you will need custom rules. Create a .semgrep/ directory at the project root:

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# .semgrep/no-env-secrets.yml
rules:
 - id: no-os-environ-secrets
 patterns:
 - pattern: os.environ[$KEY]
 - metavariable-regex:
 metavariable: $KEY
 regex: ".*(SECRET|PASSWORD|TOKEN|KEY).*"
 message: "Direct access to secrets from environment variables. Use the secrets manager."
 languages: [python]
 severity: WARNING

Then reference it in the pipeline:

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variables:
 SEMGREP_RULES: "p/owasp-top-ten p/security-audit .semgrep/"

Handling false positives

There will be false positives. That is unavoidable. What matters is how you handle them. The worst reaction is to disable the entire rule or slap allow_failure: true on the job. Instead, use inline annotations:

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# nosemgrep: python.lang.security.audit.hardcoded-password
TEST_PASSWORD = "dummy" # test fixture, not used in production

Every suppression should have a comment explaining why it is safe to ignore. No exceptions. If you cannot justify it, do not suppress it.

For broader suppressions, use .semgrepignore:

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# Exclude test fixtures
tests/fixtures/
# Exclude auto-generated code
*_generated.py

Setting up Trivy

Dependency scanning

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trivy-fs:
 stage: security
 image:
 name: aquasec/trivy:latest
 entrypoint: [""]
 script:
 - trivy fs --severity "$TRIVY_SEVERITY" --exit-code 1 --format json --output trivy-fs.json .
 artifacts:
 paths:
 - trivy-fs.json
 when: always
 rules:
 - if: $CI_PIPELINE_SOURCE == "merge_request_event"
 - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH

Trivy examines the project’s lockfiles (package-lock.json, requirements.txt, go.sum, etc.) and cross-references versions against vulnerability databases. The --exit-code 1 flag makes the job fail if it finds anything HIGH or CRITICAL.

Container image scanning

If you build Docker images, scan them before pushing to the registry:

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trivy-image:
 stage: security
 image:
 name: aquasec/trivy:latest
 entrypoint: [""]
 needs:
 - job: build-image
 artifacts: true
 script:
 - trivy image --severity "$TRIVY_SEVERITY" --exit-code 1 --format json --output trivy-image.json "$CI_REGISTRY_IMAGE:$CI_COMMIT_SHA"
 artifacts:
 paths:
 - trivy-image.json
 when: always
 rules:
 - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH

This job depends on the image build (via needs) and only runs on the main branch, not on every MR. Scanning images is slower than scanning the filesystem, so reserve that for what actually gets deployed.

IaC scanning

One often overlooked advantage of Trivy is that it also analyzes infrastructure configurations:

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trivy-iac:
 stage: security
 image:
 name: aquasec/trivy:latest
 entrypoint: [""]
 script:
 - trivy config --severity "$TRIVY_SEVERITY" --exit-code 1 --format json --output trivy-iac.json .
 artifacts:
 paths:
 - trivy-iac.json
 when: always
 rules:
 - if: $CI_PIPELINE_SOURCE == "merge_request_event"
 changes:
 - "**/*.tf"
 - "**/Dockerfile"
 - "**/*.yml"
 - "**/*.yaml"

It catches Dockerfiles running as root, Terraform files with overly open security groups, and Kubernetes configs without resource limits. The changes block ensures it only runs when relevant files are modified, avoiding unnecessary scans.

Blocking policies

Do not start blocking everything from day one. That breeds frustration, creative workarounds, and eventually someone puts allow_failure: true on every security job.

Better to do it in phases:

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# Phase 1: Report only
semgrep:
 allow_failure: true

# Phase 2: Block critical only
semgrep:
 script:
 - semgrep ci --config "$SEMGREP_RULES" --json --output semgrep-results.json
 - |
 CRITICAL=$(jq '[.results[] | select(.extra.severity == "ERROR")] | length' semgrep-results.json)
 if [ "$CRITICAL" -gt 0 ]; then
 echo "Blocked: $CRITICAL critical findings"
 exit 1
 fi
 allow_failure: false

# Phase 3: Block high + critical
# ... adjust the jq filter

Same goes for Trivy. The --severity flag already lets you control which levels block the pipeline. Start with CRITICAL only, and once the team has adapted, add HIGH.

The complete pipeline

Putting it all together:

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stages:
 - test
 - security
 - build
 - deploy

variables:
 TRIVY_SEVERITY: "HIGH,CRITICAL"
 SEMGREP_RULES: "p/owasp-top-ten p/security-audit"

semgrep:
 stage: security
 image: semgrep/semgrep:latest
 script:
 - semgrep ci --config "$SEMGREP_RULES" --json --output semgrep-results.json
 - |
 CRITICAL=$(jq '[.results[] | select(.extra.severity == "ERROR")] | length' semgrep-results.json)
 echo "Critical findings: $CRITICAL"
 if [ "$CRITICAL" -gt 0 ]; then
 echo "Pipeline blocked"
 exit 1
 fi
 artifacts:
 paths:
 - semgrep-results.json
 when: always
 rules:
 - if: $CI_PIPELINE_SOURCE == "merge_request_event"
 - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH

trivy-fs:
 stage: security
 image:
 name: aquasec/trivy:latest
 entrypoint: [""]
 script:
 - trivy fs --severity "$TRIVY_SEVERITY" --exit-code 1 --format json --output trivy-fs.json .
 artifacts:
 paths:
 - trivy-fs.json
 when: always
 rules:
 - if: $CI_PIPELINE_SOURCE == "merge_request_event"
 - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH

trivy-config:
 stage: security
 image:
 name: aquasec/trivy:latest
 entrypoint: [""]
 script:
 - trivy config --severity "$TRIVY_SEVERITY" --exit-code 1 --format json --output trivy-iac.json .
 artifacts:
 paths:
 - trivy-iac.json
 when: always
 rules:
 - if: $CI_PIPELINE_SOURCE == "merge_request_event"
 changes:
 - "**/*.tf"
 - "**/Dockerfile"
 - "**/*.yml"

trivy-image:
 stage: security
 image:
 name: aquasec/trivy:latest
 entrypoint: [""]
 needs:
 - job: build
 artifacts: true
 script:
 - trivy image --severity "$TRIVY_SEVERITY" --exit-code 1 --format json --output trivy-image.json "$CI_REGISTRY_IMAGE:$CI_COMMIT_SHA"
 artifacts:
 paths:
 - trivy-image.json
 when: always
 rules:
 - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH

Semgrep and the Trivy scans run in parallel within the security stage. If any of them fails, the pipeline stops before building or deploying.

Surfacing results in merge requests

JSON reports are fine for auditing, but developers need feedback visible directly in the MR. GitLab supports native security reports if you use official templates, but with external tools you can parse the JSON and comment on the MR:

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comment-results:
 stage: .post
 image: alpine:latest
 script:
 - apk add --no-cache curl jq
 - |
 SEMGREP_COUNT=$(jq '.results | length' semgrep-results.json 2>/dev/null || echo "0")
 TRIVY_COUNT=$(jq '.Results[]?.Vulnerabilities // [] | length' trivy-fs.json 2>/dev/null || echo "0")

 BODY="### Security summary\n- Semgrep: ${SEMGREP_COUNT} findings\n- Trivy: ${TRIVY_COUNT} vulnerabilities"

 curl --request POST \
 --header "PRIVATE-TOKEN: ${GITLAB_API_TOKEN}" \
 --header "Content-Type: application/json" \
 --data "{\"body\": \"$BODY\"}" \
 "${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/merge_requests/${CI_MERGE_REQUEST_IID}/notes"
 rules:
 - if: $CI_PIPELINE_SOURCE == "merge_request_event"
 allow_failure: true

Not the most elegant solution, but it works. If you are on GitLab Ultimate you get integrated security reports. If not, this gives enough visibility.

Cache and performance

Scans add time to the pipeline, and if that time is excessive the team will end up disabling them. A few things that help:

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trivy-fs:
 variables:
 TRIVY_CACHE_DIR: ".trivycache/"
 cache:
 key: trivy-db
 paths:
 - .trivycache/
 # ...rest of the job

Caching Trivy’s vulnerability database avoids downloading it on every run. It is roughly 40MB downloaded from GitHub, and on shared runners that download can take a while.

For Semgrep, the binary itself is already fast, but if your repository is large, limit the paths:

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semgrep:
 script:
 - semgrep ci --config "$SEMGREP_RULES" --include="src/" --include="app/" --json --output semgrep-results.json

No point scanning node_modules/, vendor/, or asset directories.

What I learned running this in practice

I have been using this setup in production for a while now, and some things only become clear with actual use.

Trivy flags a lot of CVEs in base images that have no fix available. If you do not filter with --ignore-unfixed, you will have constant noise. Better to add that flag and focus on what you can actually fix:

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trivy image --ignore-unfixed --severity HIGH,CRITICAL my-image:latest

With Semgrep, community rulesets are a good starting point, but the rules that deliver the most value are the ones you write yourself, tailored to your project’s patterns. A single rule that catches unparameterized ORM queries is worth more than a hundred generic rules.

And the most important thing: do not try to plug every hole at once. Start with scans in report-only mode, review what comes up, tune the rules, and only then start blocking. If you block everything on day one, someone will have put allow_failure: true on every job by day two.

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