SMTP Smuggling: New Flaw Lets Attackers Bypass Security and Spoof Emails
Jan 03, 2024
Cyber Threat / Email Security
A new exploitation technique called Simple Mail Transfer Protocol ( SMTP ) smuggling can be weaponized by threat actors to send spoofed emails with fake sender addresses while bypassing security measures. "Threat actors could abuse vulnerable SMTP servers worldwide to send malicious emails from arbitrary email addresses, allowing targeted phishing attacks," Timo Longin, a senior security consultant at SEC Consult, said in an analysis published last month. SMTP is a TCP/IP protocol used to send and receive email messages over a network. To relay a message from an email client (aka mail user agent), an SMTP connection is established between the client and server in order to transmit the actual content of the email. The server then relies on what's called a mail transfer agent (MTA) to check the domain of the recipient's email address, and if it's different from that of the sender, it queries the domain name system (DNS) to look up the MX (mail exchanger) rec
