  subsys(name, cb) {
    if (!this._sock || !this._sock.writable)
      throw new Error('Not connected');

    openChannel(this, 'session', (err, chan) => {
      if (err) {
        cb(err);
        return;
      }

      reqSubsystem(chan, name, (err, stream) => {
        if (err) {
          cb(err);
          return;
        }

        cb(undefined, stream);
      });
    });

    return this;
  }
The software constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.