Don't know anything about Cyberduck do you have a terminal app similar to PuTTY or SecureCRT? If you can SSH (Secure Shell) to where your files are and cd into the folder containing wp-content. You can use the following command:
chmod -R o-w wp-content
It will remove the w (write) permission from that directory and any sub-directory and the files in those directories. You really shouldn't set the execute bit (x) on files unless you need to. If you want the directories to be 755 (rwxr-xr-x), I'm guessing you want the files to be 644 (rw-r--r--).