I have set up a synced folder in Vagrant, from my Windows host to the guest. Initially the permissions on the files were too open so I added the following mount options:
I was having a similar issue with folder permissions. I'm using virtualbox on Mac OSX. I added the owner and group options which fixed my issue of not being able to write to a cache directory on the server. Update to include folder and file modes.
srv.vm.synced_folder server["synced_folder"]["src"], server["synced_folder"]["dest"], create: true, group:'vagrant', owner:'www-data', mount_options: ["dmode=775,fmode=664"]