Exim 4 before 4.94.2 allows Heap-based Buffer Overflow in queue_run via two sender options: -R and -S. This may cause privilege escalation from exim to root.
https://www.tenable.com/cyber-exposure/2021-threat-landscape-retrospective
https://www.exim.org/static/doc/security/CVE-2020-qualys/CVE-2020-28011-SPRSS.txt