thank you for your reply.
----- Original Message -----
From: "Lesley Kimmel" <ljkimmel99(a)hotmail.com>
To: "Jan Lieskovsky" <jlieskov(a)redhat.com>
Cc: "SCAP Security Guide" <scap-security-guide(a)lists.fedorahosted.org>
Sent: Thursday, June 11, 2015 3:31:14 PM
Subject: RE: RHEL6 SSG Bug (SSH,Ciphers)
Thanks for the detailed feedback. I understand the reasoning now. I also
think that it is always safest to go ahead and explicitly place those
options in the configuration files (in this case sshd_config). My concern,
though, is that without having modified sshd_config AT ALL every OVAL check
Assuming here you mean all sshd checks passed without any change being performed
to sshd_config. Can you be more specific which profile you used for scan and also
which Red Hat Enterprise Linux 6 version was this scan performed at? Was it RHEL-6.7
I will try to reproduce the behaviour in between but as much as possible concrete
details would be helpful to identify the reason quicker.
Just to confirm, the system in question having the above behaviour wasn't installed
using on of the kickstarts from the RHEL/6/kickstart directory, right? (because
in that case it would be expected all the rules would pass when performing a scan).
Typically, I run the SCAP tools once to give me a starting point and
begin fixing the Failed and Unchecked items from there. Had I not had so
much experience hardening RHEL systems I would have overlooked these sshd
configurations because they all reported as passed. I would submit that
these tests should all fail if the setting is not present and uncommented.
Also, on a more general note/question would it be possible to do a "match
all" type of scenario for configuration directives with many required
options/arguments so that it wasn't necessary to ensure that they match the
exact order specified in the OVAL check. For example, I was configuring
auditd yesterday. I copied stig.rules from /usr/share/doc/audit-<version> to
/etc/audit/rules.d. Even though the items in stig.rules meet all of the
requirements outlined in the SSG many of the checks fail because the options
aren't listed in the same order as they are in the OVAL. Here's a concrete
-a always,exit -F arch=b32 -S creat -S open -S openat -S open_by_handle_at -S
truncate -F exit=-EACCES -f auid>=500 -F auid!=4294967295 -k acess
The OVAL, in this case, checks for:
As you can tell the 'stig.rules' contains an extra syscall
(open_by_handle_at) which will cause this check to always fail unless either
the OVAL is updated or the audit rule is modified to match the check
exactly. It might make more sense to check multiple patterns and require
that they all pass:
Note the '.*' bookending the actual syscall being matched in each test.
This looks like reasonable request / enhancement. We are trying to write
audit / OVAL rules in general as tight as possible, so they wouldn't allow
invalid configurations. But on the other hand they should be flexible enough
to allow / PASS on different forms of valid configuration(s).
Although I am aware that this begins to make the OVAL content much more bulky
and we are probably trying to make it as terse as possible.
The OVAL content doesn't need to be terse. It should be readable (read as after
looking at it it should be visible what's it is doing), but doesn't necessarily
need to be short, when / where more complexity is necessary it to be appropriate.
This is probably
also a special case because most services don't include templates like
auditd. Anyway, I'm just trying to open up a discussion and possibly help
There's always space for enhancements. Couple of months ago we didn't even have
audit OVAL checks for all audit rules. Now we have them (or at least for majority
of them AFAICT), and we definitely can / should enhance them to properly handle
all the nuances of the correct configuration(s).
Let me know if I can help.
Depends on the way you are willing to help. You are helping already showing
us to see the issues not seen till now :) (or seen already, but not finding
time to address them till now).
But if you want to help even more (like want to create concrete patches and
GitHub pull requests for review), you are definitely welcome to do so
(more eyes can recognize more issues and even fix them quicker).
Thank you && Regards, Jan.
Jan iankko Lieskovsky / Red Hat Security Technologies Team
> Date: Thu, 11 Jun 2015 05:27:15 -0400
> From: jlieskov(a)redhat.com
> To: ljkimmel99(a)hotmail.com
> CC: scap-security-guide(a)lists.fedorahosted.org
> Subject: Re: RHEL6 SSG Bug (SSH,Ciphers)
> Hello Lesley,
> ----- Original Message -----
> > From: "Lesley Kimmel" <ljkimmel99(a)hotmail.com>
> > To: "SSG" <scap-security-guide(a)lists.fedorahosted.org>
> > Sent: Thursday, June 11, 2015 12:14:56 AM
> > Subject: RHEL6 SSG Bug (SSH,Ciphers)
> > All;
> > I ran into a bug in the latest SSG for RHEL6 (0.1.21-2). There is
> > definitely
> > an issue with the check for approved Ciphers. Initially the check passed
> > with no entry at all for Ciphers. I then placed a Cipher line with (1)
> > valid
> > cipher: pass. Finally I put an entry in sshd_config with a bogus cipher:
> > passed. I just ran into this at the end of my workday today so I didn't
> > get
> > much of a chance to analyze it. Plus I'm really just starting to dig into
> > the 'innards' of the content so I don't fully realize the
> > all
> > the various sections (rule/def/tst/obj/ste).
> Thank you for the report. I will have a look into this issue && report the
> findings back once obtained.
> > I'm also pretty sure that some
> > of the other checks against sshd_config are off. The check for
> > 'PermitRootLogin no' passed even though the file contains
> > '#PermitRootLogin
> > yes
> For this part it is possible the corresponding regular expression doesn't
> honours comments properly. I will double check that (btw would be good
> if you could try the very same with the most recent scap-security-guide
> 0.1.22 version from upstream's Git, since it's possible it got corrected
> in between already). But I will double check that, and report back.
> >' and typically the checks are looking for the presence of the target
> > string, not the absence of it.
> For the last part ("the checks are looking for the presence of the target
> string, not the absence of it" - this is motivated by the "nature" of
> sshd service and it's config file /etc/ssh/sshd_config.
> A bit longer story about sshd hopefully without too much gory details being
> as follows - sshd besides loading settings from /etc/sshd/sshd_config file
> honours also internal "default" options / settings. To mention an example
> "Protocol 2" directive has become a default setting starting from certain
> sshd version. The implication of these internal "default" settings being
> that in order to obtain the exact sshd configuration, that will be actually
> used, it is not sufficient to inspect the content of /etc/ssh/sshd_config
> because it will not list / contain all the settings that will be actually
> The only way how to obtain the real settings is to run the "sshd -T"
> which will print out the real settings. Since in the OVAL checks it is not
> possible to run external / arbitrary commands (this limitation is one of
> features of the OVAL language), it is not possible within sshd OVAL checks
> to run "sshd -T" to obtain final configuration, and therefore it is not
> reliably to verify if some setting is applied or not (it might be applied
> despite not being explicitly present in the /etc/ssh/sshd_config file.
> Like it is the case for the "Protocol 2" default internal setting for
> time already).
> Since we can't inspect the values of internal "default" options, the
> way how
> for sure to tell if the system is configured properly, is to require the
> being explicitly present in the /etc/ssh/sshd_config file. In other words
> we still
> require the "Protocol 2" directive to be explicitly present in the
> file even when "Protocol 2" internal setting has become
> and it's
> very unlikely some sshd setting would use "Protocol 1" version. The
> of this approach being that the sshd OVAL checks might report false
> negatives in some
> cases (system is configured properly due to the use of safe internal
> "default" value,
> but since the particular option isn't present in /etc/ssh/sshd_config [it's
> the sshd's
> default, so it's not necessary to be listed there, since it will be used
> we are reporting failure like in the case the system would be configured
> There of course is a way how to report proper sshd results - add a new
> probe to the 5.12 version of the OVAL language that would internally run
> "sshd -T"
> command when querying sshd options.
> That way we would truly inspect sshd options, that would be really applied.
> it is not a short-term solution (it takes time till the proposal is
> accepted into
> OVAL language, it takes time till the new feature is implemented, and last
> but not
> least it would work only on those OVAL scanner versions supporting OVAL
> 5.12 language
> versions. IOW till this is implemented, I am afraid we don't have a
> different option,
> just to explicitly require some option to be present in
> /etc/ssh/sshd_config even
> when this might lead to reporting false negatives in some cases).
> > Any input would be appreciated.
> Hope the above explains the background / motivations behind requiring
> of an options a bit. FWIW regarding those two reported issues (Ciphers
> check &&
> PermitRootLogin reporting PASS also with '#PermitRootLogin no' setting) I
> inspect them yet && report the findings back.
> > Thanks,
> Thank you && Regards, Jan.
> Jan iankko Lieskovsky / Red Hat Security Technologies Team
> > Les Kimmel
> > Systems Engineer, CSC
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