EC-Council
312-50V9 · Question #581
312-50V9 Question #581: Real Exam Question with Answer & Explanation
The correct answer is E: None of the above.. None of the listed options can block telnet access to port 25 without also breaking legitimate SMTP email functionality, since SMTP itself is a text-based protocol that behaves identically to a telnet session on port 25.
Question
While examining audit logs, you discover that people are able to telnet into the SMTP server on port 25. You would like to block this, though you do not see any evidence of an attack or other wrong doing. However, you are concerned about affecting the normal functionality of the email server. From the following options choose how best you can achieve this objective?
Options
- ABlock port 25 at the firewall.
- BShut off the SMTP service on the server.
- CForce all connections to use a username and password.
- DSwitch from Windows Exchange to UNIX Sendmail.
- ENone of the above.
Explanation
None of the listed options can block telnet access to port 25 without also breaking legitimate SMTP email functionality, since SMTP itself is a text-based protocol that behaves identically to a telnet session on port 25.
Common mistakes.
- A. Blocking port 25 at the firewall would drop all inbound SMTP connections, preventing legitimate email from reaching the server.
- B. Shutting off the SMTP service would completely disable email processing on the server, not just unauthorized interactive sessions.
- C. Requiring credentials does not prevent a TCP connection from being established to port 25; it only adds an authentication step after the connection is already open.
- D. Switching from Exchange to Sendmail is irrelevant because both mail server platforms accept connections on port 25 using the same text-based SMTP protocol.
Concept tested. SMTP protocol behavior and port 25 access control limitations
Reference. https://learn.microsoft.com/en-us/exchange/mail-flow/connectors/receive-connectors
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