IMO, there are two diffent issues:
(1) appending a acceptable parameter to a match block will limit the scope of the
parameter; eg:
Match User nox
X11Forwarding no
PermitRootLogin no
This will effectively be ignored.
(2) appending a non-acceptable parameter will result in a configuration error, eg:
Match User nox
X11Forwarding no
ClientAliveInterval 900
This will cause the sshd to fail at startup (or restart, if you're lucky).
Bottom line, remediation should check for Match blocks and append any changes in the
preceding lines, not at end of file.
Regards
--
Rui Pedro Bernardino
CTE2/Tecnologias e Desenvolvimento
PT Inovação
-----Original Message-----
From: scap-security-guide-bounces(a)lists.fedorahosted.org
[mailto:scap-security-guide-bounces@lists.fedorahosted.org] On Behalf Of Jan Lieskovsky
Sent: terça-feira, 17 de Dezembro de 2013 16:20
To: scap-security-guide(a)lists.fedorahosted.org
Subject: OpenSSH Match blocks / keywords handling [was Re: [PATCH] [RHEL6] Move the
closing quote in sshd disable root login remediation script at the end]
Thank you for opening this topic, Rui.
----- Original Message -----
From: "Rui Pedro Bernardino"
<rui-p-bernardino(a)ptinovacao.pt>
To: scap-security-guide(a)lists.fedorahosted.org
Sent: Tuesday, December 17, 2013 4:24:39 PM
Subject: RE: [PATCH] [RHEL6] Move the closing quote in sshd disable
root login remediation script at the end
Hi all,
Just to remind that sshd_config may have ‘Match’ blocks at the end of file.
From the manual page:
Match Introduces a conditional block. If all of the criteria on the
Match line are satisfied, the keywords on the following lines
override those set in the global section of the config file,
until either another Match line or the end of the file.
Any fixes/checks should have this into consideration… just appending
won’t work in all cases.
While this is true (current implementation doesn't take these into
account) I am not sure about the SSG upstream opinion on this (if we should check / fix
just global options or also settings included in the Match blocks).
The purpose of Match blocks / keywords in OpenSSH is to allow / have some way how to
handle different configuration requirement (in comparison to the global one) in certain
circumstances (require keys by default, but allow login via password from some concrete IP
for example). Wondering if enforcing change on configuration values also in Match blocks
could "break the settings" from the administrator's point of view.
On other hand while not changing them, might still allow selected use-cases to be less
safe than prescribed by the policy, it wouldn't touch the customs administrators got
accustomed to.
Wider opinion on this area appreciated.
Thank you && Regards, Jan.
--
Jan iankko Lieskovsky / Red Hat Security Technologies Team
Regards
--
Rui Pedro Bernardino
CTE2/Tecnologias e Desenvolvimento
PT Inovação
From: scap-security-guide-bounces(a)lists.fedorahosted.org
[mailto:scap-security-guide-bounces@lists.fedorahosted.org] On Behalf
Of David Smith
Sent: terça-feira, 17 de Dezembro de 2013 15:20
To: scap-security-guide(a)lists.fedorahosted.org
Subject: Re: [PATCH] [RHEL6] Move the closing quote in sshd disable
root login remediation script at the end
Your change makes total sense to me -- please push!
On 12/17/2013 05:08 AM, Jan Lieskovsky wrote:
When checking SSH remediation / fixes prior including them into
Fedora, noticed there's a slight typo in
RHEL6/input/fixes/bash/sshd_disable_root_login.sh:
..
echo "PermitRootLogin "no >> /etc/ssh/sshd_config ..
This by itself wouldn't cause the remediation to fail, but it to be
more consistent with form of other fixes, moved the closing quote at
the end (as assuming that's what was originally intended).
Thank you && Regards, Jan.
--
Jan iankko Lieskovsky / Red Hat Security Technologies Team
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