OpenSMTPD before 6.6.4 allows remote code execution because of an out-of-bounds read in mta_io in mta_session.c for multi-line replies. Although this vulnerability affects the client side of OpenSMTPD, it is possible to attack a server because the server code launches the client code during bounce handling.

ascii_load_sockaddr in smtpd in OpenBSD before 7.1 errata 024 and 7.2 before errata 020, and OpenSMTPD Portable before 7.0.0-portable commit f748277, can abort upon a connection from a local, scoped IPv6 address.

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.

smtpd/lka_filter.c in OpenSMTPD before 6.8.0p1, in certain configurations, allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via a crafted pattern of client activity, because the filter state machine does not properly maintain the I/O channel between the SMTP engine and the filters layer.

OpenSMTPD before 6.6.4 allows local users to read arbitrary files (e.g., on some Linux distributions) because of a combination of an untrusted search path in makemap.c and race conditions in the offline functionality in smtpd.c.