An inefficient algorithm (quadratic complexity) was found in Exiv2 before version 0.27.4. The inefficient algorithm is triggered when Exiv2 is used to write metadata into a crafted image file. An attacker could potentially exploit the vulnerability to cause a denial of service, 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 rm.