A mail service company has hired a penetration tester to conduct an enumeration of all user accounts on an SMTP server to identify whether previous staff member accounts are still active. Which of the following commands should be used to accomplish the goal?
To enumerate all user accounts on an SMTP server, the most appropriate commands to use are VRFY and EXPN. The VRFY command is used to verify if a specific email user exists on the SMTP server. This helps in identifying which email addresses are valid and in use. The EXPN command expands a mailing list to show all the addresses that are part of that list, which can further help in identifying active user accounts. These commands are specifically designed for tasks related to user enumeration on SMTP servers.
VRFY and EXPN are both SMTP commands used to verify the validity and/or obtain additional information about an email address. The VRFY command is used to verify an email address, while the EXPN command is used to obtain additional information on a specific email address such as aliases, forwarding addresses, etc.
The correct answer is A. VRFY and EXPN. The VRFY command is used to verify whether a particular user account exists on the server. It will send a response indicating whether the user exists or not. The EXPN command is used to expand a mailing list, allowing the tester to see the members of that list. Together, these two commands can be used to identify all of the user accounts that exist on the server.
Option B is incorrect because the TURN command is used to reverse the direction of an SMTP conversation, allowing the client to become the server and the server to become the client. It is not used to identify user accounts. Option C is incorrect because the EXPN command is used to expand a mailing list, not to identify user accounts. The TURN command is used to reverse the direction of an SMTP conversation, not to identify user accounts. Option D is incorrect because the RCPT TO command is used to specify the recipient of an email message, not to identify user accounts. The VRFY command is used to verify whether a particular user account exists on the server, not to specify the recipient of an email message.
A. VRFY and EXPN are the commands that should be used to accomplish the goal of enumerating all user accounts on an SMTP server. VRFY command is used to verify the existence of an email address on the SMTP server, allowing the tester to identify which email addresses are active. EXPN command is used to expand a mailing list, allowing the tester to identify which email addresses are members of a mailing list. B. VRFY and TURN: TURN is not related to SMTP commands, it's used in STUN/TURN protocols for peer-to-peer communication and it's not used in SMTP to enumerate user accounts. C. EXPN and TURN: Same as above, TURN is not related to SMTP commands D. RCPT TO and VRFY: RCPT TO is used to specify the recipient of an email and VRFY is used to verify the existence of an email address, it's not used to enumerate all user accounts on an SMTP server. It's important to note that, Many modern SMTP servers will not respond to VRFY and EXPN commands by default as they can be used for malicious purposes.
D. RCPT TO and VRFY
• VRFY: This command asks the SMTP server to verify whether a specified email address exists. • EXPN: This command asks the SMTP server to expand a mailing list or to provide information about the members of a mailing list. A. VRFY and EXPN Explanation: Using the VRFY and EXPN commands together, a penetration tester can gather information about valid user accounts and mailing lists on the SMTP server. Here’s how they work: • VRFY: When sent to the SMTP server, it checks if a specific user exists. For example: VRFY <a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="4d383e283f0d28352c203d2128632e2220">[email protected]</a> • EXPN: When sent to the SMTP server, it expands a mailing list and provides information about all the members of that list. For example: EXPN listname
TURN is obsolete and no longer works. VRFY and EXPN are similar. VRFY determines whether or not a mailbox exists on the local host. EXPN verifies whether or not a mailing list exists on the local host. Neither of these verifies whether or not the address is still active. Since we are looking for specific ex-employees, and whether or not they are still active, then RCPT TO will need to be used. Tedious, but a necessary evil in this case, I believe.
Maybe a better choice would have been EXPN and RCPT TO...?
In the context of enumerating user accounts on an SMTP server, the commands used to verify whether an address exists and to reveal the actual address when aliases are used are VRFY (Verify) and EXPN (Expand). The VRFY command checks whether a username is valid, and the EXPN command can reveal the members of a mailing list. So, the correct option is: A VRFY and EXPN
Explanation: RCPT TO is an SMTP command used to verify the email address of a recipient during the SMTP conversation. This command is used to check if an email address exists on the server. If the email address exists, the server responds with a 250 status code; otherwise, it responds with a 550 status code. VRFY is an SMTP command used to verify the existence of a particular user account on the server. If the user account exists, the server responds with a 250 status code, which indicates that the user account is valid; otherwise, it responds with a 550 status code, which indicates that the user account is invalid. By using the combination of RCPT TO and VRFY commands, the penetration tester can enumerate all the user accounts on the SMTP server and verify if they are still active or not.
https://cr.yp.to/smtp/vrfy.html