A malicious third-party can give a crafted "ssh://..." URL to an
unsuspecting victim, and an attempt to visit the URL can result in any
program that exists on the victim's machine being executed. Such a URL
could be placed in the .gitmodules file of a malicious project, and an
unsuspecting victim could be tricked into running "git clone
--recurse-submodules" to trigger the vulnerability.

Brian Neel, Joern Schneeweisz, and Jeff King discovered that Git did
not properly handle host names in 'ssh://' URLs. A remote attacker
could use this to construct a git repository that when accessed
could run arbitrary code with the privileges of the user.