During an incident investigation, a security analyst discovers the web server is generating an unusually...

Requests sent from the same IP address using different user agents are likely to be malicious or suspicious, as they indicate that an attacker is trying to evade detection or bypass security controls by changing their browser or device identification. These requests may indicate that an attacker is using automated tools or scripts to scan or attack the web server.

Requests identified by a threat intelligence service with a bad reputation are also likely to be malicious or suspicious, but they are not the source of the activity, as they originate from different IP addresses. These requests may indicate that an attacker is trying to exploit a vulnerability or perform reconnaissance on the web server.

Requests blocked by the web server per the input sanitization are not likely to be the source of the activity, as they indicate that the web server has successfully prevented an attack by validating and filtering any malicious input from the requests. These requests may indicate that an attacker is trying to inject malicious code or commands into the web server.

Failed log-in attempts against the web application are not likely to be the source of the activity, as they indicate that the web application has successfully prevented unauthorized access by verifying and rejecting any invalid credentials from the requests. These requests may indicate that an attacker is trying to guess or brute-force passwords or usernames for the web application.

Requests sent by NICs with outdated firmware are not likely to be the source of the activity, as they indicate that some devices on the network have not been updated with the latest security patches or features for their network interface cards (NICs). These requests may indicate that some devices are vulnerable to network attacks or have performance issues.

Existence of HTTP/501 status codes generated to the same IP address are not likely to be the source of the activity, as they indicate that the web server has encountered an error or does not support a request method from the client. These requests may indicate that an attacker is trying to use an invalid or unsupported method to access the web server.