Free Vulnerability Scanning Tools: Top Open-Source Options Compared
Written by the Rafter Team
Free vulnerability scanning tools give you real security coverage without licensing costs. Trivy, ZAP, Semgrep, and OWASP Dependency-Check are the most widely adopted open-source options, each targeting a different layer of your stack. The right combination depends on whether you need container scanning, web app testing, static analysis, or dependency checking.
No single free tool covers every vulnerability class. Open-source scanners excel at known patterns but lack deep taint analysis, AI-code detection, and unified dashboards that commercial platforms provide.
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Four Tools at a Glance
| Tool | Type | What It Scans | Best For |
|---|---|---|---|
| Trivy | SCA / Container | Container images, filesystems, IaC, SBOM | DevOps teams scanning containers in CI |
| OWASP ZAP | DAST | Running web applications | Testing deployed apps for injection and misconfig |
| Semgrep | SAST | Source code (30+ languages) | Developers writing custom static analysis rules |
| OWASP Dependency-Check | SCA | Dependency manifests (Java, .NET, Node) | Java-heavy teams tracking CVEs in libraries |
Trivy
Trivy scans container images, filesystems, and IaC templates for known vulnerabilities and misconfigurations. It pulls from multiple vulnerability databases and returns results in seconds with zero configuration.
Strengths: Fast scans, broad coverage across OS packages and language dependencies, Kubernetes and Terraform support, SBOM generation.
Limitations: No source code analysis — it checks packages and configs, not your application logic. Limited custom rule support.
OWASP ZAP
ZAP is a DAST proxy that intercepts HTTP traffic and runs automated attack payloads against discovered endpoints. It catches SQL injection, XSS, CSRF, and server misconfigurations.
Strengths: Extensive plugin ecosystem, scriptable via Python/JavaScript, authentication handling for testing behind login pages.
Limitations: Requires a running application. Cannot analyze source code. Generates false positives on modern SPAs.
Semgrep
Semgrep performs lightweight static analysis by matching code patterns defined in YAML rules. The open-source engine supports 30+ languages with community rulesets covering OWASP Top 10 patterns.
Strengths: Fast execution, easy custom rules without AST knowledge, language-agnostic pattern syntax, strong CI/CD integration.
Limitations: Open-source version lacks cross-file taint analysis. Secrets scanning and the Pro ruleset require a paid license.
OWASP Dependency-Check
Dependency-Check identifies known CVEs in your project dependencies by comparing package identifiers against the NVD.
Strengths: Deep NVD integration, mature Java/JVM ecosystem support, CI-friendly reporting.
Limitations: High false-positive rate due to CPE matching heuristics. Limited language coverage outside the JVM ecosystem.
Feature Comparison
| Capability | Trivy | ZAP | Semgrep | Dependency-Check |
|---|---|---|---|---|
| Source code analysis | No | No | Yes | No |
| Dependency CVE detection | Yes | No | Paid only | Yes |
| Container image scanning | Yes | No | No | No |
| Web app testing (DAST) | No | Yes | No | No |
| IaC scanning | Yes | No | Community rules | No |
| Custom rules | Limited | Scripts/plugins | Yes (YAML) | No |
| CI/CD integration | Strong | Moderate | Strong | Moderate |
| Cross-file taint analysis | No | N/A | Paid only | No |
Where Free Tools Fall Short
Free scanners cover known patterns well. They leave gaps in three areas.
No unified view. Four tools means four dashboards and no correlation between findings. A dependency CVE flagged by Trivy might only be exploitable through a code path that Semgrep cannot trace across files.
AI-generated code blind spots. None of these tools detect patterns specific to AI-assisted development — hallucinated API calls, insecure defaults, or prompt injection vectors.
No prioritization. Free tools report CVEs without business context or reachability analysis.
Rafter combines static analysis, dependency scanning, and secrets detection in a single CI pipeline — with cross-file taint tracking and AI-code pattern detection that free tools cannot provide.