- djm@cvs.openbsd.org 2014/04/18 23:52:25

     [compat.c compat.h sshconnect2.c sshd.c version.h]
     OpenSSH 6.5 and 6.6 have a bug that causes ~0.2% of connections
     using the curve25519-sha256@libssh.org KEX exchange method to fail
     when connecting with something that implements the spec properly.

     Disable this KEX method when speaking to one of the affected
     versions.

     reported by Aris Adamantiadis; ok markus@

1 files changed, 16 insertions, 2 deletions

diff --git a/compat.c b/compat.c
index 9d9fabef3..64f9790a8 100644
--- a/compat.c
+++ b/compat.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: compat.c,v 1.82 2013/12/30 23:52:27 djm Exp $ */
+/* $OpenBSD: compat.c,v 1.83 2014/04/18 23:52:25 djm Exp $ */
 /*
  * Copyright (c) 1999, 2000, 2001, 2002 Markus Friedl.  All rights reserved.
  *
@@ -95,6 +95,8 @@ compat_datafellows(const char *version)
                 { "Sun_SSH_1.0*",       SSH_BUG_NOREKEY|SSH_BUG_EXTEOF},
                 { "OpenSSH_4*",         0 },
                 { "OpenSSH_5*",         SSH_NEW_OPENSSH|SSH_BUG_DYNAMIC_RPORT},
+                { "OpenSSH_6.5*,"
+                  "OpenSSH_6.6",        SSH_NEW_OPENSSH|SSH_BUG_CURVE25519PAD},
                 { "OpenSSH*",           SSH_NEW_OPENSSH },
                 { "*MindTerm*",         0 },
                 { "2.1.0*",             SSH_BUG_SIGBLOB|SSH_BUG_HMAC|
@@ -251,7 +253,6 @@ compat_cipher_proposal(char *cipher_prop)
         return cipher_prop;
 }
 
-
 char *
 compat_pkalg_proposal(char *pkalg_prop)
 {
@@ -265,3 +266,16 @@ compat_pkalg_proposal(char *pkalg_prop)
         return pkalg_prop;
 }
 
+char *
+compat_kex_proposal(char *kex_prop)
+{
+        if (!(datafellows & SSH_BUG_CURVE25519PAD))
+                return kex_prop;
+        debug2("%s: original KEX proposal: %s", __func__, kex_prop);
+        kex_prop = filter_proposal(kex_prop, "curve25519-sha256@libssh.org");
+        debug2("%s: compat KEX proposal: %s", __func__, kex_prop);
+        if (*kex_prop == '\0')
+                fatal("No supported key exchange algorithms found");
+        return kex_prop;
+}
+