CKEditor window can be resized if the resize plugin is enabled. You can however define the minimum and maximum dimensions to prevent the editor window from becoming too small or too big to handle.

To define the minimum editor dimensions after resizing, specify the resize_minWidth and resize_minHeight values in pixels.

config.resize_minWidth = 300;
config.resize_minHeight = 300;

To define the maximum editor dimensions after resizing, specify the resize_maxWidth and resize_maxHeight values in pixels.

config.resize_maxWidth = 800;
config.resize_maxHeight = 600;