CVE-2021-29457: Heap-based Buffer Overflow

Exiv2 is a command-line utility and C++ library for reading, writing, deleting, and modifying the metadata of image files. A heap buffer overflow was found in Exiv2 versions v0.27.3 and earlier. The heap overflow is triggered when Exiv2 is used to write metadata into a crafted image file. An attacker could potentially exploit the vulnerability to gain code execution, if they can trick the victim into running Exiv2 on a crafted image file. Note that this bug is only triggered when _writing_ the metadata, which is a less frequently used Exiv2 operation than _reading_ the metadata. For example, to trigger the bug in the Exiv2 command-line application, you need to add an extra command-line argument such as `insert`. The bug is fixed in version v0.27.4.