Among the most basic and fundamental promises that open source software provides is that code is open and can be forked to create another project. That promise, however, can sometimes run into challenges, especially if the code in question wasn't actually open source to begin with.

A public and ugly fight is taking place between infrastructure-as-code- vendor Hashicorp and its Linux Foundation-backed open source fork known as OpenTofu.

Here's the story so far, and how it's changing today.

Hashicorp develops the Terraform infrastructure as code technology, which from its inception in 2014 until August 2023 was available under the open source Mozilla Public License v2.0 (MPL v2). For business reasons, Hashicorp changed Terraform's license to a non-open source initiative OSI compliant source-available license known as the Business Source License (BSL).

That change led to widespread community concern, sparking the creation of the OpenTF project as an open source fork. OpenTF was rebranded as OpenTofu in September 2023 and brought under the wing of the Linux Foundation.  In January, the first stable release of OpenTofu was made generally available by the Linux Foundation and that's where the new spate of legal accusations began.

On April 3, lawyers for Hashicorp sent the Linux Foundation a legal cease-and-desist letter over alleged violations in OpenTofu where code was in appropriately used from Hashicorp.

“Our investigation shows that OpenTofu has used HashiCorp code made available only under BSL license terms in violation of those terms,” the letter states.

In a response from OpenTofu's legal council being made public today, the open source fork of Terraform vehemently denied and rebuked Hashicorp's accusations.

“Your Letter fundamentally misrepresents the source code origination (SCO) history and nature of the OpenTofu project (Project) and therefore it erroneously complains of violations of HashiCorp's intellectual property right that simply did not occur,” the OpenTofu lawyers letter states.

The use of the term “SC”' is a double entendre by the OpenTofu lawyers that has a very specific connotation that few (if any) in the open source community, including HashiCorp, would ever miss.

Back in 2003 The SCO Group, which was a Unix operating system vendor, filed a lawsuit against IBM and Linux as a whole, arguing that Linux infringed on Unix copyrights. That legal battle ended very poorly for SCO, which is a company that no longer exists, while on the other hand IBM and Linux have prospered over the last two decades.

At the core of the dispute is code that HashiCorp claims is licensed under the BSL and not the actual open source Mozilla Public License. The BSL provides open access to code for users, but restricts access for commercial vendors for a period of time.

OpenTofu's lawyers argue that the code that is used in the OpenTofu project is entirely and only based on the pre-BSL code and is all still available under the Mozilla Public License (MPL)

“To my client's knowledge, none of the Terraform code subject to the BSL has been improperly copied, incorrectly sourced, or used for any purpose,” the lawyer's letter states.

Now here's where the drama spikes further. Not only are the OpenTofu lawyers refuting HashiCorp's claims, they are also warning HashiCorp that it might have violated open source licensing rules, too.

“We expect that your developers have similar policies and process in place to ensure newly created or modified MPL-2.0 source code in OpenTofu is not used or included in any Terraform BSL-licenses source code files, as such a combination could violate the terms of the MPL-2.0 license and infringe OpenTofu copyright.”

Game on.