The structure 无…不… (wú…bù…) is a classic double negative pattern in Chinese that creates a strong positive assertion. It means “There is no… that is not…” or more simply, “every…”. Therefore, 无孔不入 (wú kǒng bù rù) literally means “There is no hole that is not entered,” which creates the powerful meaning of “entering every single hole,” or being completely pervasive.
This idiom is common in both spoken and written Chinese, often to express frustration or criticism.