Exim Internet Mail Vulnerabilities

Number: AL17-013
Date: 28 November 2017


The purpose of this alert is to bring attention to recently disclosed vulnerabilities in Exim Internet Mailer.


CCIRC has become aware of two vulnerabilities in Exim Internet Mailer version 4.88 and 4.89 that allows remote attackers to execute arbitrary code or cause a denial of service (use-after-free) via vectors involving BDAT commands.

Suggested Action

Due to the potential risk presented by this vulnerability, CCIRC recommends that system administrators monitor for the developer released security fix. Additional mitigation advice has been published by the vendor.

Furthermore, CCIRC is providing a Suricata rule to detect BDAT command that attempt to exploit those vulnerabilities.

alert smtp any any -> $HOME_NET any (msg: "[PT OPEN] Exim 4.88, 4.89 UAF RCE Attempt (CVE-2017-16943)"; flow: established, to_server; content: "BDAT"; content: "BDAT"; within: 10; pcre: "/BDAT\s*\D[^\n\r]*[\n\r][^\n\r]{100}/"; reference: cve, 2017-16943; reference: url, bugs.exim.org/show_bug.cgi?id=2199; classtype: attempted-admin; sid: 10002280; rev: 2; )


Note to Readers

In support of Public Safety's mission to build a safe and resilient Canada, CCIRC's mandate is to help ensure the security and resilience of the vital non-federal government cyber systems that underpin Canada's national security, public safety and economic prosperity. As Canada's computer security incident response team, CCIRC is Canada's national coordination centre for the prevention and mitigation of, preparedness for, response to, and recovery from cyber incidents on non-federal government systems. It does this by providing authoritative advice and support, and coordinating information sharing and incident response.

Please note, CCIRC PGP key has recently been updated.

For general information, please contact Public Safety Canada's Public Affairs division at:

Telephone: 613-944-4875 or 1-800-830-3118
Fax: 613-998-9589
E-mail: ps.communications-communications.sp@canada.ca

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