upstream commit

Cap DH-GEX group size at 4kbits for Cisco implementations.
 Some of them will choke when asked for preferred sizes >4k instead of
 returning the 4k group that they do have.  bz#2209, ok djm@

Upstream-ID: 54b863a19713446b7431f9d06ad0532b4fcfef8d

1 files changed, 4 insertions, 1 deletions

diff --git a/kexgexc.c b/kexgexc.c
index 3f20491c4..71ff13352 100644
--- a/kexgexc.c
+++ b/kexgexc.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kexgexc.c,v 1.21 2015/04/13 02:04:08 djm Exp $ */
+/* $OpenBSD: kexgexc.c,v 1.22 2015/05/26 23:23:40 dtucker Exp $ */
 /*
  * Copyright (c) 2000 Niels Provos.  All rights reserved.
  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
@@ -28,6 +28,7 @@
 
 #ifdef WITH_OPENSSL
 
+#include <sys/param.h>
 #include <sys/types.h>
 
 #include <openssl/dh.h>
@@ -65,6 +66,8 @@ kexgex_client(struct ssh *ssh)
         kex->min = DH_GRP_MIN;
         kex->max = DH_GRP_MAX;
         kex->nbits = nbits;
+        if (datafellows & SSH_BUG_DHGEX_LARGE)
+                kex->nbits = MIN(kex->nbits, 4096);
         /* New GEX request */
         if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST)) != 0 ||
             (r = sshpkt_put_u32(ssh, kex->min)) != 0 ||