As you may know, ModSecurity is licensed under GPL version 2. This licence has served us reasonably well, but there’s been one problem that has been following us for a long time. I chose to use the GPLv2 for ModSecurity, back in day, mostly in order to prevent the use of ModSecurity in proprietary derivative works. This strategy worked, but it had an unfortunate side effect of also preventing creation of open source derivative works due to the incompatibility between the Apache Software License version 2 and the GPLv2. The problem eventually caused the removal of ModSecurity from Debian.
After the GPLv3 was introduced we had an option to switch to it (the incompatibility with the ASLv2 was fixed), but doing that would require a significant investment to fully understand the new licence and the consequences of its use. (Decisions were easier to make when I was the only person making them; now there are quite a few people involved.) The fact that GPLv3 hasn’t been proven in practice does not help. At some point we realised that the path to fixing the problem was not through the licence change, but through an exception that would grant additional rights to qualifying open source projects. The exception creates additional rights for those who choose to accept it, but it does not change the licence of ModSecurity itself, which remains licensed under GPLv2. Changes and improvements to ModSecurity must still comply with the GPLv2.
Anyway, the final draft of the exception is ready: ModSecurity_Licensing_Exception_1.0-draft5.pdf . Here’s a brief overview:
- You want to package a web server distribution based on Apache and you want to include ModSecurity in it. The Exception allows you to do this for as long as all the components use the approved open source licences.
- If you make changes or improvements to ModSecurity, or write code that links with it—either directly or indirectly (e.g. through a third component)—such code must be released under GPLv2; it cannot be covered by the Exception.
- If you build a user interface to control the derivative work (and thus ModSecurity too) you can choose any approved open source licence for it.
The plan for now is to give you some time to send us feedback, if you wish. If everything goes well, the next stable version of ModSecurity will include the Exception too.