Answer by Rocksn17 for How to include files outside of Docker's build context?

As is described in this GitHub issue the build actually happens in /tmp/docker-12345, so a relative path like ../relative-add/some-file is relative to /tmp/docker-12345. It would thus search for /tmp/relative-add/some-file, which is also shown in the error message.*

It is not allowed to include files from outside the build directory, so this results in the "Forbidden path" message."