Exim 4 before 4.94.2 allows Out-of-bounds Read because pdkim_finish_bodyhash does not validate the relationship between sig->bodyhash.len and b->bh.len; thus, a crafted DKIM-Signature header might lead to a leak of sensitive information from process memory.
https://www.tenable.com/cyber-exposure/2021-threat-landscape-retrospective
https://www.exim.org/static/doc/security/CVE-2020-qualys/CVE-2020-28025-BHASH.txt