At which stage attacking the vulnerability belongs in Cyber kill chain?

Exploitation is the specific Cyber Kill Chain phase where the adversary executes code or triggers a flaw to gain access to the target. This is the stage where the vulnerability is directly attacked - the weapon crafted during Weaponization and delivered in the Delivery phase is activated against the target system.

Reconnaissance is the initial information-gathering phase focused on researching the target, not the stage where vulnerabilities are actively exploited.

Weaponization involves coupling an exploit with a payload to create a deliverable weapon, which occurs before the vulnerability is actually triggered on the target.

Delivery is the transmission of the weaponized payload to the target environment (e.g., phishing email or USB), not the stage where the vulnerability itself is attacked.