A person described as vulnerable in a general way is someone who is easily hurt or harmed physically, mentally, or emotionally. Vulnerable can also describe a person, group, or thing that is open to attack, harm, or damage. Both senses of vulnerable are often followed by the preposition to.
It is common to feel especially vulnerable in the wake of major change.
The patient will be most vulnerable to infection immediately after surgery.
Your computer is vulnerable to viruses without the proper antivirus software.