What is open source software? Open source software (OSS) is software distributed with its source code publicly available under a license that lets anyone view, modify, and redistribute it. The category spans the Linux kernel, which reportedly powers all 500 of the world's fastest supercomputers on the TOP500 list, down to single-purpose npm packages with a dozen lines of code. It is no longer an alternative to commercial software — it is the substrate underneath it. Synopsys' 2024 Open Source Security and Risk Analysis (OSSRA) report scanned 1,067 commercial codebases and found open source in 96% of them, averaging 526 open source components per application. Package registries confirm the scale: npm hosts more than 3 million packages, and PyPI passed 500,000 projects in 2023. Before a security team can manage open source risk, it has to understand the open source software meaning in practice: what OSS actually is, how licensing works, and where the real exposure sits — which is what this glossary entry covers.
What Is Open Source Software, Exactly?
Open source software is code released under a license that grants users the right to run, study, modify, and redistribute it, with the original source code included rather than just a compiled binary. This open source software meaning is the one maintained by the Open Source Initiative (OSI), the nonprofit that has approved over 100 licenses as meeting its ten-point Open Source Definition since the term was coined in 1998. The distinction matters because "source-available" is not the same thing: code like early versions of Elastic's license or MongoDB's Server Side Public License (SSPL) lets you see the source but restricts commercial use, which the OSI does not classify as open source. Common OSS examples include the Linux kernel (1991), the Apache HTTP Server (1995), PostgreSQL (1996), and the Kubernetes container orchestrator that Google open-sourced in 2014. Open source is also not synonymous with "free" in the zero-cost sense — the OSI's own framing is "free as in freedom," not "free as in beer" — a distinction that matters commercially, since companies like Red Hat and Elastic have built billion-dollar businesses selling support and hosting around freely licensed code.
What's the Difference Between Open Source and Closed Source Software?
The difference is visibility and control: closed source (proprietary) software ships only as a compiled binary, with the vendor retaining exclusive rights to the source code, while open source ships the source itself under a license granting broad reuse rights. That trade-off cuts both ways for security. Open source lets any researcher audit the code — which is how the OpenSSL Heartbleed bug (CVE-2014-0160) was found by independent researchers at Codenomicon and Google in April 2014 — but it also means attackers can read the same code for free, study it for exploitable patterns, and in some cases contribute to the project themselves, as happened with the XZ Utils backdoor. Closed source software gets audited only by the vendor or by security researchers working from the compiled binary, which raises the cost of finding bugs but doesn't eliminate them; it simply means the public rarely sees the code review history.
What Makes a License "Open Source" Versus Proprietary?
A license qualifies as open source only if it satisfies the OSI's ten criteria, which include free redistribution, availability of source code, and no discrimination against fields of use. In practice, OSS licenses split into two families. Permissive licenses — MIT, Apache 2.0, and BSD — let you use, modify, and relicense the code with minimal obligations, and they dominate the modern ecosystem: GitHub's own license usage data has consistently shown MIT as the single most-used license across public repositories, followed by Apache 2.0. Copyleft licenses — GPLv2, GPLv3, and AGPLv3 — require that derivative works be distributed under the same license, which is why companies like MongoDB and Elastic moved away from AGPL-style terms toward SSPL in 2018–2021 to close what they called a "cloud loophole" that let hyperscalers resell their databases as managed services without contributing back.
How Much of Modern Software Actually Runs on Open Source?
The overwhelming majority of it does — 96% of codebases scanned in the 2024 Synopsys OSSRA report contained open source, and in sectors like computer hardware and semiconductors that figure reached 100%. A single widely used component can end up embedded in hundreds of thousands of downstream projects: Google's Open Source Insights project has tracked Apache Log4j 2 as a dependency of more than 400,000 public GitHub repositories. On the JavaScript side, npm alone serves tens of billions of package downloads per week across its 3-million-plus package registry. This concentration means that a single maintainer's decision, a single compromised credential, or a single unpatched CVE in a low-level utility library can ripple into an enormous number of production applications simultaneously — which is exactly what happened with Log4Shell in December 2021.
What Security Risks Come With Using Open Source Components?
The core risks are known vulnerabilities in dependencies, malicious code inserted into legitimate packages, and compromise of the maintainers or build infrastructure that produce them. Log4Shell (CVE-2021-44228), disclosed on December 9, 2021, scored a maximum CVSS of 10.0 and allowed unauthenticated remote code execution in any application logging attacker-controlled strings through a vulnerable Log4j 2 version — Cloudflare recorded over 400,000 exploitation attempts within the first 24 hours of disclosure. The XZ Utils backdoor (CVE-2024-3094), discovered by a Microsoft engineer on March 29, 2024, showed the maintainer-compromise variant: a contributor who had built trust over roughly two years inserted an SSH-authentication bypass into the liblzma library, narrowly caught before it reached major Linux distributions. The 2018 event-stream npm incident, where a malicious actor added a bitcoin-wallet-stealing dependency called flatmap-stream after gaining maintainer access to a package with 2 million weekly downloads, and the 2024 polyfill.io attack, where a sold domain began serving malware to an estimated 100,000+ websites that still referenced the script, both show that dependency risk isn't limited to unpatched CVEs — trust in the supply chain itself is the attack surface.
How Do Security Teams Track and Manage Open Source Risk?
Security teams track open source risk primarily through Software Bills of Materials (SBOMs) and software composition analysis (SCA) tooling that inventories every dependency, transitive or direct, in an application. The push toward SBOMs accelerated after Executive Order 14028, signed May 12, 2021, directed U.S. federal agencies to require them from software vendors, and the NTIA published its "minimum elements" specification for SBOMs the same year. Two formats dominate: CycloneDX, maintained by OWASP, and SPDX, which became an ISO/IEC standard (5962:2021) in 2021. An SBOM only reduces risk if it's paired with continuous vulnerability matching against feeds like the National Vulnerability Database and OSV, plus prioritization logic — because a dependency inventory with thousands of entries and no way to tell which ones are actually reachable from running code just becomes another unread report.
What Types of Open Source Software Exist, and How Do Teams Govern Them?
Open source software isn't a single category — it spans operating systems (Linux, FreeBSD), web and application servers (Apache, Nginx), databases (PostgreSQL, MySQL), and the enormous long tail of individual libraries and frameworks that make up the bulk of a typical dependency tree. Understanding these types of open source software matters because the risk profile differs: a foundational OS-level component gets far more scrutiny than a single-maintainer utility library buried five levels deep in a transitive dependency graph. As organizations scale their open source usage, informal tracking stops working, and teams turn to dedicated open source license management software — often the same platform that runs SCA scanning — to enforce which licenses are approved, flag copyleft obligations before they create legal exposure, and maintain an audit trail to satisfy open source compliance management software requirements imposed by customers or regulators. This is the practical side of open source software governance: policies that define which licenses are allowed, who can approve exceptions, and how new dependencies get reviewed before they ship. Mature open source development in software engineering treats license review as part of the same pipeline as vulnerability scanning, not a separate legal exercise that happens after the fact.
FAQ
Is open source software license management the same as open source license management software?
Same idea, different emphasis. Open source software license management is the practice — tracking obligations, approving licenses, flagging copyleft risk. Open source license management software is the tooling that automates it. Most compliance teams need both: a defined policy and a platform (often the same one running SCA) that enforces it against every dependency automatically rather than through a manual spreadsheet review.
How Safeguard Helps
Safeguard turns open source inventory into an actionable, prioritized backlog instead of a wall of CVE noise. Our platform generates and ingests SBOMs in both CycloneDX and SPDX formats, giving teams a single source of truth for every open source component across their codebases and containers. Reachability analysis then determines which flagged vulnerabilities sit in code paths your application actually executes, cutting the triage list down from every CVE in a dependency tree to the ones that are exploitable in practice. Griffin AI layers on top to explain each finding in context and recommend a remediation path, and where a safe upgrade exists, Safeguard opens an auto-fix pull request so engineering teams can ship the patch without manually chasing version bumps across dozens of repositories.