Here are examples of the word/phrase "vulnerable" used in a sentence and paraphrased in a sentence...
Don't let your guard down or you will be vulnerable.
Don't let your guard down or you will be susceptible.
You will become vulnerable once you step outside of the barrier's range.
You will become susceptible once you step outside of the barrier's range.
With his armor he is invincible but without it he is vulnerable.
With his armor he is invincible but without it he is susceptible.
Other Examples...