The remote Debian host is missing a security-related update.
Etienne Stalmans discovered that git, a fast, scalable, distributed revision control system, is prone to an arbitrary code execution vulnerability exploitable via specially crafted submodule names in a .gitmodules file.
Upgrade the git packages. For the oldstable distribution (jessie), this problem has been fixed in version 1:2.1.4-2.1+deb8u6. For the stable distribution (stretch), this problem has been fixed in version 1:2.11.0-3+deb9u3.