A security researcher has discovered and publicly disclosed two critical vulnerabilities in the popular Internet mail message transfer agent Exim, one of which could allow a remote attacker to execute malicious code on the targeted server. The first vulnerability, identified as CVE-2017-16943, is a use-after-free bug which could be exploited to remotely execute arbitrary code in the SMTP server by crafting a sequence of BDAT commands. The second vulnerability, identified as CVE-2017-16944, is a denial of service (DoS) flaw that could allow a remote attacker to hang Exim servers even the connection is closed by forcing it to run in an infinite loop without crashing. Both vulnerabilities reside in Exim version 4.88 and 4.89, and sysadmins are recommended to update their mail transfer agent application Exim version 4.90 released on GitHub.