libgit2 versions v0.27.0 through v1.9.0 built with the libssh2 SSH backend (USE SSH=libssh2) contain a shell command injection vulnerability that allows remote attackers to execute arbitrary commands on an SSH server by supplying a repository path containing unescaped shell metacharacters such as single quotes, semicolons, or pipes. The gen proto() function in ssh libssh2.c inserts the repository path directly into a shell command string without escaping special characters before passing it to libssh2 channel exec(), enabling an attacker to craft a malicious submodule URL in a .gitmodules file that, when processed during a recursive clone, causes the remote server's shell to interpret injected commands under the victim's SSH user account.