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From 6d0faf6dc76ac8cc73d6f8e478db7c97f7013a2d Mon Sep 17 00:00:00 2001
From: Colin Watson <cjwatson@debian.org>
Date: Sun, 9 Feb 2014 16:10:18 +0000
Subject: Various Debian-specific configuration changes
ssh: Enable ForwardX11Trusted, returning to earlier semantics which cause
fewer problems with existing setups (http://bugs.debian.org/237021).
ssh: Set 'SendEnv LANG LC_*' by default (http://bugs.debian.org/264024).
ssh: Enable HashKnownHosts by default to try to limit the spread of ssh
worms.
ssh: Enable GSSAPIAuthentication and disable GSSAPIDelegateCredentials by
default.
Document all of this, along with several sshd defaults set in
debian/openssh-server.postinst.
Author: Russ Allbery <rra@debian.org>
Forwarded: not-needed
Last-Update: 2015-11-29
Patch-Name: debian-config.patch
---
readconf.c | 2 +-
ssh.1 | 21 +++++++++++++++++++++
ssh_config | 7 ++++++-
ssh_config.5 | 19 ++++++++++++++++++-
sshd_config.5 | 25 +++++++++++++++++++++++++
5 files changed, 71 insertions(+), 3 deletions(-)
diff --git a/readconf.c b/readconf.c
index c0ba5a7..e4e1cba 100644
--- a/readconf.c
+++ b/readconf.c
@@ -1749,7 +1749,7 @@ fill_default_options(Options * options)
if (options->forward_x11 == -1)
options->forward_x11 = 0;
if (options->forward_x11_trusted == -1)
- options->forward_x11_trusted = 0;
+ options->forward_x11_trusted = 1;
if (options->forward_x11_timeout == -1)
options->forward_x11_timeout = 1200;
if (options->exit_on_forward_failure == -1)
diff --git a/ssh.1 b/ssh.1
index 05b7f10..649d6c3 100644
--- a/ssh.1
+++ b/ssh.1
@@ -755,6 +755,16 @@ directive in
.Xr ssh_config 5
for more information.
.Pp
+(Debian-specific: X11 forwarding is not subjected to X11 SECURITY extension
+restrictions by default, because too many programs currently crash in this
+mode.
+Set the
+.Cm ForwardX11Trusted
+option to
+.Dq no
+to restore the upstream behaviour.
+This may change in future depending on client-side improvements.)
+.Pp
.It Fl x
Disables X11 forwarding.
.Pp
@@ -763,6 +773,17 @@ Enables trusted X11 forwarding.
Trusted X11 forwardings are not subjected to the X11 SECURITY extension
controls.
.Pp
+(Debian-specific: This option does nothing in the default configuration: it
+is equivalent to
+.Dq Cm ForwardX11Trusted No yes ,
+which is the default as described above.
+Set the
+.Cm ForwardX11Trusted
+option to
+.Dq no
+to restore the upstream behaviour.
+This may change in future depending on client-side improvements.)
+.Pp
.It Fl y
Send log information using the
.Xr syslog 3
diff --git a/ssh_config b/ssh_config
index 228e5ab..c9386aa 100644
--- a/ssh_config
+++ b/ssh_config
@@ -17,9 +17,10 @@
# list of available options, their meanings and defaults, please see the
# ssh_config(5) man page.
-# Host *
+Host *
# ForwardAgent no
# ForwardX11 no
+# ForwardX11Trusted yes
# RhostsRSAAuthentication no
# RSAAuthentication yes
# PasswordAuthentication yes
@@ -48,3 +49,7 @@
# VisualHostKey no
# ProxyCommand ssh -q -W %h:%p gateway.example.com
# RekeyLimit 1G 1h
+ SendEnv LANG LC_*
+ HashKnownHosts yes
+ GSSAPIAuthentication yes
+ GSSAPIDelegateCredentials no
diff --git a/ssh_config.5 b/ssh_config.5
index 5bc04b0..aaa435a 100644
--- a/ssh_config.5
+++ b/ssh_config.5
@@ -74,6 +74,22 @@ Since the first obtained value for each parameter is used, more
host-specific declarations should be given near the beginning of the
file, and general defaults at the end.
.Pp
+Note that the Debian
+.Ic openssh-client
+package sets several options as standard in
+.Pa /etc/ssh/ssh_config
+which are not the default in
+.Xr ssh 1 :
+.Pp
+.Bl -bullet -offset indent -compact
+.It
+.Cm SendEnv No LANG LC_*
+.It
+.Cm HashKnownHosts No yes
+.It
+.Cm GSSAPIAuthentication No yes
+.El
+.Pp
The configuration file has the following format:
.Pp
Empty lines and lines starting with
@@ -721,7 +737,8 @@ token used for the session will be set to expire after 20 minutes.
Remote clients will be refused access after this time.
.Pp
The default is
-.Dq no .
+.Dq yes
+(Debian-specific).
.Pp
See the X11 SECURITY extension specification for full details on
the restrictions imposed on untrusted clients.
diff --git a/sshd_config.5 b/sshd_config.5
index 7e40a27..92c23bc 100644
--- a/sshd_config.5
+++ b/sshd_config.5
@@ -57,6 +57,31 @@ Arguments may optionally be enclosed in double quotes
.Pq \&"
in order to represent arguments containing spaces.
.Pp
+Note that the Debian
+.Ic openssh-server
+package sets several options as standard in
+.Pa /etc/ssh/sshd_config
+which are not the default in
+.Xr sshd 8 .
+The exact list depends on whether the package was installed fresh or
+upgraded from various possible previous versions, but includes at least the
+following:
+.Pp
+.Bl -bullet -offset indent -compact
+.It
+.Cm ChallengeResponseAuthentication No no
+.It
+.Cm X11Forwarding No yes
+.It
+.Cm PrintMotd No no
+.It
+.Cm AcceptEnv No LANG LC_*
+.It
+.Cm Subsystem No sftp /usr/lib/openssh/sftp-server
+.It
+.Cm UsePAM No yes
+.El
+.Pp
The possible
keywords and their meanings are as follows (note that
keywords are case-insensitive and arguments are case-sensitive):
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