untrusted comment: signature from openbsd 5.5 base secret key
RWRGy8gxk9N934pTioJ2iLNiNPkO7oWbSptmBgAwU7cFTb+E8QPTRyYo02PCCJS0RFJcb4TObp6JZ+fCMoCs5KSXEhjmVzVgmwk=

OpenBSD 5.5 errata 7, June 6, 2014: Sendmail was not properly closing file
descriptions before executing programs. This could enable local users to
interfere with an open SMTP connection.

Apply patch using:

    signify -Vep /etc/signify/openbsd-55-base.pub -x 007_sendmail.patch.sig \
	-m - | (cd /usr/src && patch -p0)

And then rebuild and install sendmail:
	cd gnu/usr.sbin/sendmail
	make obj
	make depend
	make
	make install

Index: gnu/usr.sbin/sendmail/sendmail/conf.c
===================================================================
RCS file: /cvs/src/gnu/usr.sbin/sendmail/sendmail/conf.c,v
retrieving revision 1.37
diff -u -p -r1.37 conf.c
--- gnu/usr.sbin/sendmail/sendmail/conf.c	7 Feb 2014 21:25:00 -0000	1.37
+++ gnu/usr.sbin/sendmail/sendmail/conf.c	5 Jun 2014 10:15:53 -0000
@@ -5309,8 +5309,8 @@ closefd_walk(lowest, fd)
 */
 
 void
-sm_close_on_exec(highest, lowest)
-	int highest, lowest;
+sm_close_on_exec(lowest, highest)
+	int lowest, highest;
 {
 #if HASFDWALK
 	(void) fdwalk(closefd_walk, &lowest);