The remote Debian host is missing a security-related update.
Matviy Kotoniy reported that the gdImageCreateFromGifCtx() function used to load images from GIF format files in libgd2, a library for programmatic graphics creation and manipulation, does not zero stack allocated color map buffers before their use, which may result in information disclosure if a specially crafted file is processed.
Upgrade the libgd2 packages. For the oldstable distribution (jessie), this problem has been fixed in version 2.1.0-5+deb8u10. For the stable distribution (stretch), this problem has been fixed in version 2.2.4-2+deb9u1.