The Changelog for version 1.2.1 says: Fixed a regression caused by
1.2.0[6] in which decompressing corrupt JPEG images (specifically,
images in which the component count was erroneously set to a large
value) would cause libjpeg-turbo to segfault.
A Heap-based buffer overflow was found in the way libjpeg-turbo
decompressed certain corrupt JPEG images in which the component count
was erroneously set to a large value. An attacker could create a
specially-crafted JPEG image that, when opened, could cause an
application using libpng to crash or, possibly, execute arbitrary code
with the privileges of the user running the application.