An unusual steganographic technique that an attacker can use to implant a malicious webshell on unsuspecting websites has been spotted in Latin America. The technique can be used to compromise even a fully patched, up-to-date website with no obvious vulnerabilities just by uploading an image to a website. An adversary is implanting PHP code into JPEG files EXIF headers in order to upload malware onto targeted websites. The last known instance of similar technique was seen in the wild in 2013, but it is, however, rare.
Source: https://threatpost.com/rare-steganography-hack-can-compromise-fully-patched-websites/146701/