php: Heap buffer over-read in exif_scan_thumbnail()

When PHP EXIF extension is parsing EXIF information from an image, e.g. via exifreaddata function, in PHP versions 7.1.x below 7.1.31, 7.2.x below 7.2.21 and 7.3.x below 7.3.8 it is possible to supply it with data what will cause it to read past the allocated buffer. This may lead to information...