smtpd/table.c in OpenSMTPD before 6.8.0p1 lacks a certain regfree, which might allow attackers to trigger a "very significant" memory leak via messages to an instance that performs many regex lookups.
https://www.mail-archive.com/misc%40opensmtpd.org/msg05188.html
https://security.gentoo.org/glsa/202105-12
https://github.com/openbsd/src/commit/79a034b4aed29e965f45a13409268290c9910043