Language: Go
Label: vulnerable
CWE: CWE-22 \u2014 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

Code:
func (fsys MapFsImpl) OpenAtEnd(path string) (fs.File, error) {
	var file = fstest.MapFile{
		Data: []byte("content2"),
	}
	fsys.MapFS[path] = &file

	result, err := fsys.MapFS.Open(path)
	return WritableFile{result, fsys.MapFS, path}, err
}