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SMTP User Enumeration

in#bug

SMTP stands for Simple Mail Transfer Protocol is a TCP/IP protocol for sending E-mail messages between servers.SMTP usually is implemented to operate over Internet port 25. Nmap (Network Mapper) is the most popular port scanner which is designed to probe a server or host for open ports. The following are the open ports that I identified on Open-xchange’s Sandbox domain sandbox.open-xchange.com (185.27.181.34) 1-6dAjkWuijQ37qF4ZQcOzhg.png Port Scanning Via Nmap

The SMTP user enumeration can be performed automatically via Metasploit, smtp_enum module will connect to a given mail server and use a wordlist to enumerate users that are present on the remote system. 1-4JrIZEfESUViJ4qRvgOw9A.png SMTP User Enumeration Via Metasploit

This leakage can be avoided by disallowing the execution of the commands EXPN,VRFY and RCPT. 1-ilqZDnPm4YFXayGn7nIh7g.png

After reporting this issue, Open-xchange resolved the vulnerability and rewarded me the bounty and it was my first bug bounty :)

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