This bug is present in exif_process_IFD_in_MAKERNOTE method of ext/exif/exif.c file.
Detailed description and steps to reproduce for this bug is present in bug report submitted to php.net.
Bug Report : https://bugs.php.net/bug.php?id=77563
PHP version : 7.1.26
CVE-ID : 2019-9638
Uninitialized data may leak data from memory.