Apply by doing:
        cd /usr/src
        patch -p0 < 020_radius.patch

Then rebuild and install login_radius:
        cd libexec/login_radius
        make clean
        make
        make install

Index: libexec/login_radius/raddauth.c
===================================================================
RCS file: /cvs/src/libexec/login_radius/raddauth.c,v
retrieving revision 1.16
retrieving revision 1.16.2.1
diff -u -p -r1.16 -r1.16.2.1
--- libexec/login_radius/raddauth.c	10 Mar 2004 21:30:27 -0000	1.16
+++ libexec/login_radius/raddauth.c	11 Sep 2004 21:06:56 -0000	1.16.2.1
@@ -131,7 +131,7 @@ typedef struct {
 void servtimeout(int);
 in_addr_t get_ipaddr(char *);
 in_addr_t gethost(void);
-int rad_recv(char *, char *);
+int rad_recv(char *, char *, u_char *);
 void parse_challenge(auth_hdr_t *, char *, char *);
 void rad_request(pid_t, char *, char *, int, char *, char *);
 void getsecret(void);
@@ -278,7 +278,7 @@ retry:
 		rad_request(req_id, userstyle, passwd, auth_port, vector,
 		    pwstate);
 
-		switch (i = rad_recv(_pwstate, challenge)) {
+		switch (i = rad_recv(_pwstate, challenge, vector)) {
 		case PW_AUTHENTICATION_ACK:
 			/*
 			 * Make sure we don't think a challenge was issued.
@@ -437,11 +437,13 @@ rad_request(pid_t id, char *name, char *
  * Receive UDP responses from the radius server
  */
 int
-rad_recv(char *state, char *challenge)
+rad_recv(char *state, char *challenge, u_char *req_vector)
 {
 	auth_hdr_t auth;
 	socklen_t salen;
 	struct sockaddr_in sin;
+	u_char recv_vector[AUTH_VECTOR_LEN], test_vector[AUTH_VECTOR_LEN];
+	MD5_CTX context;
 
 	salen = sizeof(sin);
 
@@ -456,6 +458,16 @@ rad_recv(char *state, char *challenge)
 
 	if (sin.sin_addr.s_addr != auth_server)
 		errx(1, "bogus authentication server");
+
+	/* verify server's shared secret */
+	memcpy(recv_vector, auth.vector, AUTH_VECTOR_LEN);
+	memcpy(auth.vector, req_vector, AUTH_VECTOR_LEN);
+	MD5Init(&context);
+	MD5Update(&context, (u_char *)&auth, ntohs(auth.length));
+	MD5Update(&context, auth_secret, strlen(auth_secret));
+	MD5Final(test_vector, &context);
+	if (memcmp(recv_vector, test_vector, AUTH_VECTOR_LEN) != 0)
+		errx(1, "shared secret incorrect");
 
 	if (auth.code == PW_ACCESS_CHALLENGE)
 		parse_challenge(&auth, state, challenge);