Exim 4 before 4.94.2 allows Use After Free in smtp_reset in certain situations that may be common for builds with OpenSSL.
https://www.tenable.com/cyber-exposure/2021-threat-landscape-retrospective
https://www.exim.org/static/doc/security/CVE-2020-qualys/CVE-2020-28018-OCORK.txt
http://www.openwall.com/lists/oss-security/2021/05/12/3
http://www.openwall.com/lists/oss-security/2021/05/12/2
http://www.openwall.com/lists/oss-security/2021/05/11/6
http://www.openwall.com/lists/oss-security/2021/05/11/5
http://www.openwall.com/lists/oss-security/2021/05/11/17