Apply by doing:
	cd /usr/src
	patch -p0 < 008_fd.patch

Rebuild your kernel.

And then rebuild and install authpf:
	cd usr.sbin/authpf
	make obj
	make
	make install

Index: sys/sys/proc.h
===================================================================
RCS file: /cvs/src/sys/sys/proc.h,v
retrieving revision 1.77
retrieving revision 1.77.2.1
diff -u -p -r1.77 -r1.77.2.1
--- sys/sys/proc.h	10 Mar 2005 17:26:10 -0000	1.77
+++ sys/sys/proc.h	30 Dec 2005 01:28:02 -0000	1.77.2.1
@@ -144,7 +144,8 @@ struct	proc {
 	int	p_flag;			/* P_* flags. */
 	u_char	p_os;			/* OS tag */
 	char	p_stat;			/* S* process status. */
-	char	p_pad1[2];
+	char	p_pad1[1];
+	u_char	p_descfd;		/* if not 255, fdesc permits this fd */
 
 	pid_t	p_pid;			/* Process identifier. */
 	LIST_ENTRY(proc) p_hash;	/* Hash chain. */
Index: sys/kern/kern_descrip.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_descrip.c,v
retrieving revision 1.69
retrieving revision 1.69.4.1
diff -u -p -r1.69 -r1.69.4.1
--- sys/kern/kern_descrip.c	22 Jul 2004 06:13:08 -0000	1.69
+++ sys/kern/kern_descrip.c	30 Dec 2005 01:28:02 -0000	1.69.4.1
@@ -1220,6 +1220,17 @@ dupfdopen(fdp, indx, dfd, mode, error)
 	int error;
 {
 	struct file *wfp;
+
+	/*
+	 * Assume that the filename was user-specified; applications do
+	 * not tend to opens of /dev/fd/# when they can just call dup()
+	 */
+	if ((curproc->p_flag & (P_SUGIDEXEC | P_SUGID))) {
+		if (curproc->p_descfd == 255)
+			return (EPERM);
+		if (curproc->p_descfd != curproc->p_dupfd)
+			return (EPERM);
+	}
 
 	/*
 	 * If the to-be-dup'd fd number is greater than the allowed number
Index: sys/kern/kern_exec.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_exec.c,v
retrieving revision 1.91
retrieving revision 1.91.2.1
diff -u -p -r1.91 -r1.91.2.1
--- sys/kern/kern_exec.c	9 Mar 2005 17:41:29 -0000	1.91
+++ sys/kern/kern_exec.c	30 Dec 2005 01:28:02 -0000	1.91.2.1
@@ -634,6 +634,10 @@ sys_execve(p, v, retval)
 	if (p->p_emul && p->p_emul->e_proc_exit &&
 	    p->p_emul != pack.ep_emul)
 		(*p->p_emul->e_proc_exit)(p);
+
+	p->p_descfd = 255;
+	if ((pack.ep_flags & EXEC_HASFD) && pack.ep_fd < 255)
+		p->p_descfd = pack.ep_fd;
 
 	/*
 	 * Call exec hook. Emulation code may NOT store reference to anything
Index: usr.sbin/authpf/authpf.c
===================================================================
RCS file: /cvs/src/usr.sbin/authpf/authpf.c,v
retrieving revision 1.89
retrieving revision 1.89.2.1
diff -u -p -r1.89 -r1.89.2.1
--- usr.sbin/authpf/authpf.c	10 Feb 2005 04:24:15 -0000	1.89
+++ usr.sbin/authpf/authpf.c	18 Dec 2005 04:18:25 -0000	1.89.2.1
@@ -92,6 +92,7 @@ main(int argc, char *argv[])
 	struct in6_addr	 ina;
 	struct passwd	*pw;
 	char		*cp;
+	gid_t		 gid;
 	uid_t		 uid;
 	char		*shell;
 	login_cap_t	*lc;
@@ -257,10 +258,16 @@ main(int argc, char *argv[])
 		fclose(pidfp);
 	} while (1);
 
+	/* whack the group list */
+	gid = getegid();
+	if (setgroups(1, &gid) == -1) {
+		syslog(LOG_INFO, "setgroups: %s", strerror(errno));
+		do_death(0);
+	}
+
 	/* revoke privs */
 	seteuid(getuid());
 	setuid(getuid());
-
 	openlog("authpf", LOG_PID | LOG_NDELAY, LOG_DAEMON);
 
 	if (!check_luser(PATH_BAN_DIR, luser) || !allowed_luser(luser)) {
@@ -633,6 +640,7 @@ change_filter(int add, const char *luser
 	char	*fdpath = NULL, *userstr = NULL, *ipstr = NULL;
 	char	*rsn = NULL, *fn = NULL;
 	pid_t	pid;
+	gid_t	gid;
 	int	s;
 
 	if (luser == NULL || !luser[0] || ipsrc == NULL || !ipsrc[0]) {
@@ -674,6 +682,11 @@ change_filter(int add, const char *luser
 	case -1:
 		err(1, "fork failed");
 	case 0:
+		/* revoke group privs before exec */
+		gid = getgid();
+		if (setregid(gid, gid) == -1) {
+			err(1, "setregid");
+		}
 		execvp(PATH_PFCTL, pargv);
 		warn("exec of %s failed", PATH_PFCTL);
 		_exit(1);