Hackers can take advantage of a logical flaw in WhatsApp for Android and modify or replace media files available in external storage before the intended recipient can see them. The same risk exists with the Telegram messaging app if configured to save files to a public directory that any app can access and write to, such as the photo gallery folder. Both messaging apps provide end-to-end encryption, but this protection does not apply beyond their Android’s internal storage slot, where data cannot be reached by other apps.
Source: https://www.bleepingcomputer.com/news/security/hackers-could-modify-whatsapp-media-files-before-you-see-them/