A successful exploit is a piece of software or code that takes advantage of a vulnerability and executes malicious actions on the target system. A vulnerability is a weakness or flaw in a software or hardware component that can be exploited by an attacker. A successful exploit is one that achieves its intended goal, such as gaining unauthorized access, executing arbitrary code, escalating privileges, or compromising data.

In the given options, only B is an example of a successful exploit, because it involves a user executing code that exploits a vulnerability on a local service, such as a web server, a database, or a network protocol. This could allow the attacker to gain control over the service, access sensitive information, or perform other malicious actions.

Option A is not a successful exploit, because it involves connecting unknown media to an endpoint that copied malware due to Autorun. Autorun is a feature that automatically runs a program or script when a removable media, such as a USB drive, is inserted into a computer. This feature can be abused by malware authors to spread their malicious code, but it is not an exploit in itself. The malware still needs to exploit a vulnerability on the endpoint to execute its payload and cause damage.

Option C is not a successful exploit, because it involves identifying vulnerable services on a server. This is a step in the reconnaissance phase of an attack, where the attacker scans the target system for potential vulnerabilities that can be exploited. However, this does not mean that the attacker has successfully exploited any of the vulnerabilities, or that the vulnerabilities are even exploitable.

Option D is not a successful exploit, because it involves executing a process executable for well-known and signed software. This is a legitimate action that does not exploit any vulnerability or cause any harm. Well-known and signed software are programs that are widely used and trusted, and have a digital signature that verifies their authenticity and integrity. Executing such software does not pose a security risk, unless the software itself is malicious or compromised.