Command injection via partial submodule override

Command injection in gitoxide before 0.5.21, gix-submodule before 0.29.0, and gix before 0.84.0 allows attackers to supply shell commands. gix_submodule::File::update reads the update value from attacker-controlled .gitmodules, but its trust guard accepts any same-named section from local .git/config without verifying that the value came from that trusted section. Exploitation requires a previously initialized submodule and a downstream gix consumer that calls Submodule::update() and executes the returned command; the gix CLI does not implement submodule update.