To solve this question, the user needs to know about common web server vulnerabilities. The user must identify the vulnerability among the given options.

Now, let's go through each option and explain why it is right or wrong:

A. Limited user accounts: This option is not a common web server vulnerability. Limited user accounts may prevent unauthorized access to the web server, which is actually a security feature.

B. Default installation: This option is a common web server vulnerability. Many web servers are configured with default settings, which may include default user accounts, passwords, and configurations. Attackers can exploit these vulnerabilities to gain unauthorized access to the web server.

C. Open shares: This option is not a common web server vulnerability. Open shares are more often associated with file servers and network shares, rather than web servers.

D. No directory access: This option is not a common web server vulnerability. No directory access may prevent unauthorized access to sensitive directories on the web server, which is actually a security feature.

The Answer is: B