20 Million Trusted Domains Vulnerable to Email Hosting Exploits

Researchers found three novel, chainable email attack techniques—SPF abuse, DKIM abuse via feedback loops, and an expanded SMTP smuggling variant—that exploit misconfigurations and RFC violations in email-hosting providers to bypass SPF/DKIM/DMARC and deliver spoofed emails from potentially millions of trusted domains; they will disclose affected vendors and detection/mitigation guidance (including Message-ID correlation and enforcing RFC authentication) at Black Hat.