upstream commit

Remove support for pre-authentication compression. Doing
compression early in the protocol probably seemed reasonable in the 1990s,
but today it's clearly a bad idea in terms of both cryptography (cf. multiple
compression oracle attacks in TLS) and attack surface.

Moreover, to support it across privilege-separation zlib needed
the assistance of a complex shared-memory manager that made the
required attack surface considerably larger.

Prompted by Guido Vranken pointing out a compiler-elided security
check in the shared memory manager found by Stack
(http://css.csail.mit.edu/stack/); ok deraadt@ markus@

NB. pre-auth authentication has been disabled by default in sshd
for >10 years.

Upstream-ID: 32af9771788d45a0779693b41d06ec199d849caf

1 files changed, 2 insertions, 2 deletions

diff --git a/sshconnect2.c b/sshconnect2.c
index 5e7d07dc5..a633e76cb 100644
--- a/sshconnect2.c
+++ b/sshconnect2.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshconnect2.c,v 1.248 2016/09/22 02:29:57 dtucker Exp $ */
+/* $OpenBSD: sshconnect2.c,v 1.249 2016/09/28 16:33:07 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  * Copyright (c) 2008 Damien Miller.  All rights reserved.
@@ -174,7 +174,7 @@ ssh_kex2(char *host, struct sockaddr *hostaddr, u_short port)
             compat_cipher_proposal(options.ciphers);
         myproposal[PROPOSAL_COMP_ALGS_CTOS] =
             myproposal[PROPOSAL_COMP_ALGS_STOC] = options.compression ?
-            "zlib@openssh.com,zlib,none" : "none,zlib@openssh.com,zlib";
+            "zlib@openssh.com,none" : "none,zlib@openssh.com";
         myproposal[PROPOSAL_MAC_ALGS_CTOS] =
             myproposal[PROPOSAL_MAC_ALGS_STOC] = options.macs;
         if (options.hostkeyalgorithms != NULL) {