Exim Mail Server User-After-Free RCE | MSSP Advisory

A user-after-free vulnerability in Exim mail servers allows remote code execution during TLS shutdown when processing chunked SMTP traffic. The flaw affects the mail transfer agent used by millions of servers worldwide for email routing and delivery. Attackers can exploit this without authentication by sending specially crafted SMTP messages.

Your clients running on-premises email servers or Linux distributions with default Exim installations face immediate remote takeover risk from unauthenticated attackers. If client mail servers get compromised through this vector and you knew about it but said nothing, you own that conversation with leadership about why their email infrastructure became an attack platform.

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