The dmarc_process function in dmarc.c in Exim before 4.82.1, when EXPERIMENTAL_DMARC is enabled, allows remote attackers to execute arbitrary code via the From header in an email, which is passed to the expand_string function.
https://lists.exim.org/lurker/message/20140528.122536.a31d60a4.en.html
http://www.openwall.com/lists/oss-security/2021/05/04/7
http://git.exim.org/exim.git/commitdiff/5b7a7c051c9ab9ee7c924a611f90ef2be03e0ad0