I am a contributor to a very old project presently in violation of the GPL. Our project is a plugin for a closed-source program, but the GPL does not permit this kind of linking. The project should have been licensed under the LGPL instead, but the original authors were not aware of this.
Relicensing is already covered in another question, so we will ignore that here.
There are only about 30 contributors to the project, but it's almost ten years old at this point. Many have moved on to other projects.
The contributors clearly intended for their work to be used with the closed-source program in question. They did not know the GPL forbade it. It is exceedingly unlikely that one of them will take legal action against the project.
If the project continues despite the GPL violation, what is our legal exposure to third parties? Can the FSF or any other group sue us?