Description: Attempt SSHFP lookup even if server presents a certificate
 If an ssh server presents a certificate to the client, then the client does
 not check the DNS for SSHFP records. This means that a malicious server can
 essentially disable DNS-host-key-checking, which means the client will fall
 back to asking the user (who will just say "yes" to the fingerprint,
 sadly).
 .
 This is CVE-2014-2653.
Author: Damien Miller <djm@mindrot.org>
Reviewed-by: Matthew Vernon <matthew@debian.org>
Bug-Debian: http://bugs.debian.org/742513
Forwarded: not-needed
Last-Update: 2014-04-03

Index: b/sshconnect.c
===================================================================
--- a/sshconnect.c
+++ b/sshconnect.c
@@ -1110,29 +1110,39 @@
 {
 	int flags = 0;
 	char *fp;
+	Key *plain = NULL;
 
 	fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
 	debug("Server host key: %s %s", key_type(host_key), fp);
 	xfree(fp);
 
-	/* XXX certs are not yet supported for DNS */
-	if (!key_is_cert(host_key) && options.verify_host_key_dns &&
-	    verify_host_key_dns(host, hostaddr, host_key, &flags) == 0) {
-		if (flags & DNS_VERIFY_FOUND) {
-
-			if (options.verify_host_key_dns == 1 &&
-			    flags & DNS_VERIFY_MATCH &&
-			    flags & DNS_VERIFY_SECURE)
-				return 0;
-
-			if (flags & DNS_VERIFY_MATCH) {
-				matching_host_key_dns = 1;
-			} else {
-				warn_changed_key(host_key);
-				error("Update the SSHFP RR in DNS with the new "
-				    "host key to get rid of this message.");
+	if (options.verify_host_key_dns) {
+		/*
+		 * XXX certs are not yet supported for DNS, so downgrade
+		 * them and try the plain key.
+		 */
+		plain = key_from_private(host_key);
+		if (key_is_cert(plain))
+			key_drop_cert(plain);
+		if (verify_host_key_dns(host, hostaddr, plain, &flags) == 0) {
+			if (flags & DNS_VERIFY_FOUND) {
+				if (options.verify_host_key_dns == 1 &&
+				    flags & DNS_VERIFY_MATCH &&
+				    flags & DNS_VERIFY_SECURE) {
+					key_free(plain);
+					return 0;
+				}
+				if (flags & DNS_VERIFY_MATCH) {
+					matching_host_key_dns = 1;
+				} else {
+					warn_changed_key(plain);
+					error("Update the SSHFP RR in DNS "
+					    "with the new host key to get rid "
+					    "of this message.");
+				}
 			}
 		}
+		key_free(plain);
 	}
 
 	return check_host_key(host, hostaddr, options.port, host_key, RDRW,
