A penetration tester is performing active reconnaissance on a target web application. During the process, the tester notices that several requests return a '503 Service Unavailable' error even though the service is known to be operational and accessible to regular users. What is the MOST likely reason the tester is seeing these 503 errors?
The tester has discovered a previously unknown service vulnerability that causes the service to crash upon scanning.
The intrusion detection system (IDS) or web application firewall (WAF) is rate-limiting or blocking the tester's IP due to the reconnaissance activities.
The web server is misconfigured, resulting in intermittent responses to the tester's requests.
The web application is under maintenance, causing legitimate service interruptions.