  Welch--Gong (WG) is a hardware-oriented LFSR-based stream cipher. WG-7 is a
version of the eStream submission Welch--Gong, used for RFID encryption and
authentication purposes. It offers 80-bit cryptographic security. In modern
days, almost all ciphers achieve the security by exploiting the nonlinear
feedback structure. In this paper, we investigate the security of the nonlinear
feedback-based initialization phase of the WG-7 stream cipher using the
conventional bit-based division property of cube attack, by considering the
cipher in a non-blackbox polynomial setting. In our work, we mount the cube
attack using mixed-integer-linear-programming(MILP) models. The results of our
attack enable us to recover the secret key of WG-7 after 20 rounds of
initialization utilizing $2^{10}$ keystream bits in $2^{73}$ time. We show that
our proposed attack takes significantly lower data complexity. To the best of
our knowledge, our attack is the first one that investigates the security of
the nonlinear feedback-based initialization phase of WG-7 cipher.
