The vulnerability stems from improper neutralization of the 'url' parameter when constructing git commands. The GitHub issue example shows user input being directly concatenated into a shell command (git remote add [url]), enabling arbitrary command execution via shell operators. This matches the CWE-77 pattern where user input flows into command execution contexts without proper sanitization. The core git command execution handler in ungit's codebase (likely in a file like src/git-api.js) would be responsible for this vulnerable pattern.