What is copyleft?
Copyleft is a licensing method that uses copyright law to guarantee that software remains free and open for everyone to use, modify, and share. This means when you distribute software under a copyleft license, you must give the same freedoms to anyone who receives it.
The term "copyleft" was created by Richard Stallman in the 1980s as part of the GNU Project. It's a play on "copyright" because it reverses the traditional purpose—instead of restricting what people can do with software, copyleft ensures those freedoms are preserved forever.
Here's how it works: if you take copyleft software, modify it, and distribute your version, you must release your changes under the same copyleft license. However, terms vary by license family—GPL v2, GPL v3, LGPL, MPL, and AGPL each define different scopes and triggers for these obligations. This creates a "viral" effect where the license spreads to any code that gets combined with the original copyleft software when that combined work is distributed or offered as a service (for AGPL).
Copyleft isn't anti-copyright—it actually uses copyright law strategically. The original creator holds the copyright but grants specific permissions with conditions attached. This legal framework ensures that improvements to the software benefit the entire community rather than being locked away in proprietary products.
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Copyleft vs copyright vs permissive licenses
Understanding copyleft requires knowing how it differs from traditional copyright and permissive open-source licenses. Each approach gives users different rights and obligations.
Copyright represents the default legal protection for creative works. When someone creates software, they automatically own exclusive rights to copy, distribute, and modify it. This is the "all rights reserved" model where using the work without permission is illegal.
Copyleft flips this concept by using copyright law to enforce sharing. You can use, modify, and distribute the software freely, but any derivative works must be released under the same copyleft license. This ensures the software stays open and free for everyone.
Permissive licenses like MIT, Apache, and BSD also grant broad freedoms to use and modify software. Apache 2.0 includes an explicit patent license grant, providing additional legal protection that MIT and BSD licenses don't offer. However, they don't require derivative works to remain open source. You can take permissive-licensed code and incorporate it into proprietary software without sharing your modifications.
The key difference lies in downstream obligations. Copyleft prioritizes keeping the software itself free, while permissive licenses prioritize giving developers maximum freedom to do whatever they want with the code.
Types of copyleft licenses and their implications
Copyleft licenses exist on a spectrum from "strong" to "weak" based on how strictly they enforce sharing requirements. Understanding these differences helps you assess compliance risks.
Strong copyleft licenses like the GNU General Public License (GPL v2, GPL v3) have broad sharing requirements. If your proprietary code becomes a derivative work of GPL code and you distribute the combined work, that derivative work must be licensed under the GPL. The derivative work analysis—including whether static or dynamic linking creates a derivative work—is fact-dependent and varies by jurisdiction. Consult legal counsel for your specific situation.
Weak copyleft licenses such as the Lesser GPL (LGPL v2.1, LGPL v3) and Mozilla Public License (MPL 2.0) offer more flexibility. You can typically link proprietary software to these libraries without open-sourcing your proprietary code. However, modifications to the LGPL or MPL-covered components themselves must be shared under the same license.
Network copyleft licenses like the Affero GPL (AGPL v3) address SaaS usage. While GPL obligations are generally tied to distribution, AGPL requires offering the Corresponding Source of the AGPL-covered program to users who interact with it over a network. This means if you modify AGPL software and offer it as a service, you must provide the modified source code to your users.
The scope also matters:
Full copyleft applies to the derivative work that includes the covered code. However, mere aggregation—such as bundling independent programs on the same storage medium or in the same distribution—does not create a derivative work and thus does not generally trigger the GPL obligation for the independent programs.
Partial copyleft may only cover specific parts, allowing other components to use different licenses
Legal and business risks of copyleft in cloud environments
Legal exposure represents the biggest threat. When you combine proprietary code with strong copyleft software, and then distribute that combined work or make it available over a network (AGPL), you're legally required to release your proprietary source code under the same license. This can turn valuable intellectual property into free, open-source software overnight.
Supply chain contamination happens when copyleft licenses enter through transitive dependencies. According to the 2025 Black Duck Open Source Security and Risk Analysis report, 30% of license conflicts stem from these hidden dependencies. Modern applications rely on hundreds of third-party libraries, with 64% being transitive dependencies (Black Duck 2024 OSSRA), making manual tracking impossible.
Container and microservices risks multiply in layered architectures. A copyleft-licensed component in a container image can impose obligations for that covered component and any derivative works upon distribution. However, packaging unrelated works in the same container image does not, by itself, create a derivative work under most copyleft licenses. Code-to-cloud correlation helps identify which running services, container images, and development teams own affected components, enabling you to trace violations back to the source repository, specific commit, and responsible developer for rapid remediation. The boundaries between microservices can blur when determining derivative work status. Whether inter-service communication (via APIs, message queues, or RPC) creates a derivative work is fact-specific and legally unsettled. Consult legal counsel when evaluating copyleft obligations in microservices architectures.
M&A due diligence risks can derail deals when copyleft violations surface during code audits. Acquiring companies scrutinize license compliance as part of their technical due diligence process. Undisclosed strong copyleft usage—especially GPL or AGPL components embedded in proprietary products—can collapse negotiations entirely or trigger significant valuation reductions due to potential IP exposure. Demonstrating mature governance requires automated SBOM generation, complete chain of custody documentation for every component, and evidence of consistent policy enforcement throughout the development lifecycle.
Copyleft compliance strategies for modern software development
Managing copyleft risks requires automated systems that integrate compliance into your development workflow. Manual processes can't keep up with modern software development speeds.
Automated scanning forms the foundation of compliance. Software Composition Analysis (SCA) tools automatically scan code repositories, container images, and build artifacts to identify all open-source components and their licenses. Agentless discovery across repositories, registries, and cloud workloads ensures full coverage of direct and transitive dependencies without operational overhead or performance impact on production systems. Integrating these tools into CI/CD pipelines ensures no code deploys without license verification.
Policy as code lets you define and enforce licensing rules automatically. Security and legal teams create policies specifying which licenses are approved, which need review, and which are forbidden. A unified policy engine applies these allow/deny lists consistently across IDEs, pull request checks, CI/CD gates, and deployment-time validation, eliminating policy drift and ensuring every environment enforces the same rules.
Sample license policy matrix
Use this starter template and customize with your legal team:
| License Category | Examples | Policy | Use Cases |
|---|---|---|---|
| Approved | MIT, Apache 2.0, BSD-3-Clause | Auto-approve | All use cases |
| Review Required | MPL 2.0, LGPL 3.0, EPL 2.0 | Manual approval | Dynamic linking only |
| Restricted | GPL v2, GPL v3, AGPL v3 | Forbidden for distributed products | Internal tools only (with approval) |
| Unknown/Custom | Proprietary, unlicensed | Block until legal review | Requires counsel assessment |
Important: This is a starting template. Work with legal counsel to tailor policies to your business model, distribution methods, and risk tolerance. Document exceptions and maintain an approval register for audit trails.
Developer education creates your first line of defense. Provide clear guidelines about open-source licensing, explain the differences between license types, and share your company's policies. When developers understand the risks, they make better decisions upfront.
Architectural boundaries help isolate risky components. Design applications using microservices or dynamic linking to reduce coupling between copyleft and proprietary components. However, technical isolation alone is not a legal guarantee—derivative work analysis depends on legal interpretation, not just technical architecture.
Documentation practices require maintaining accurate Software Bills of Materials (SBOMs) for every application using industry-standard formats like SPDX or CycloneDX. Automate SBOM generation in your CI/CD pipeline using tools like Syft, CycloneDX CLI, or native package manager plugins. Attach SBOMs to release artifacts, container images, and deployment manifests, and sign them using tools like Sigstore Cosign to support audit trails and M&A due diligence. SBOMs also provide evidence for SOC 2 CC7 (vendor management) and ISO 27001 Annex A.15 (supplier relationships) controls.
Legal review processes establish clear workflows for handling exceptions. When developers need restricted components, formal review processes assess risks and document decisions properly—a necessity given that 33% of codebases contain open-source components with no license or customized licenses requiring legal review, according to the 2025 Black Duck Open Source Security and Risk Analysis report.
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How Wiz Code helps manage copyleft license risks across the software supply chain
Wiz Code automatically discovers copyleft licenses in your direct and transitive dependencies across repositories and container images. This gives you complete visibility into your open-source usage without manual tracking.
The unified policy engine prevents prohibited copyleft licenses from reaching production through customizable CI/CD pipeline guardrails. You can set rules that automatically block deployments containing restricted licenses or require approval workflows for specific cases.
Wiz Security Graph correlates license risks with network exposure, identity reach, and sensitive data access to surface toxic combinations—for example, a GPL-licensed component in an internet-exposed service with admin privileges to customer databases. This graph-based prioritization helps you focus on the license issues that pose the highest real business risk, not just every finding.
Cloud-to-code traceability maps running workloads with copyleft components back to specific repositories and developers for rapid remediation. When you discover a compliance issue in production, you know exactly where to fix it.
IDE and pull request integrations provide immediate feedback to developers about non-compliant licenses within their existing workflows. This shift-left approach catches issues early when they're cheapest and easiest to fix.
Agentless scanning ensures complete visibility into copyleft usage across VMs, containers, and serverless functions without performance impact. You get comprehensive coverage of your entire cloud environment automatically.
Ready to shift your open-source governance from reactive audits to continuous, cloud-native compliance? See how Wiz Code delivers agentless, code-to-cloud visibility and graph-based risk prioritization in a live demo.
Legal Disclaimer: This article provides educational information about open-source license compliance. Open-source license obligations are fact-specific, jurisdiction-dependent, and subject to legal interpretation. This content does not constitute legal advice. Always consult qualified legal counsel for guidance on your specific situation, license interpretations, and compliance strategies.
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