Do you need a full source tree for this ? IIRC major Linux distros do this via preliminary disclosure to a private mailing list possibly with a patch attached.
That way distros can do a local build to verify the patch works and fixes the issue & they then apply the patch in their public infra right after the embargo runs out.
That way distros can do a local build to verify the patch works and fixes the issue & they then apply the patch in their public infra right after the embargo runs out.