I am using EncFS with a USB drive. How secure is this if my USB drive gets stolen? I ask because the .encfs6.xml file is saved in the USB drive and I can open it with a normal text editor. Do I need to be concerned that the .encfs6.xml can easily be opened with a text editor if the USB drive is stolen?
In addition to clear-text configuration settings, the EncFS configuration file also contains the volume key, but that key is encrypted with the master key, which is derived from your password.
In other words, it is not possible to decrypt anything without the password.
The password you set for the encrypted directory, is your last bastion to your data. The xml file you mention is only describing your encryption setup but not leaking information: the algorithm you use and how you are using it, is not part of the secret.
If you lose the USB, and you have a strong passphrase (meaning a long password) as a master key, your data will be secure to a dictionary try to mount it. Choose your password based on the risk. Evaluate what happens in the stolen scenario (worse than loss). An usb we could say is one of the most exposed, but it's like a phone or a cloud directory.