Re: Why exclude unset auid in STIG rules

Re: Why exclude unset auid in STIG rules

[Steve Grubb]

On Wednesday, May 11, 2016 06:28:11 PM Wyatt, Curtis wrote:
> I don't understand why the STIG audit rules have -F auid!=4294967295 in it. 
> If auid is unset, why wouldn't you still want to see the events in the
> logs?

When a user logs in, the auid gets set to the uid that they used to login 
with. Daemons are not user sessions and have the loginuid set to  -1. The auid 
representation is an unsigned 32 bit integer. So, -1 becomes 4294967295. The 
rules use a directive like this: -F auid>=1000 to trigger on user activity. It 
turns out that would trigger on daemons doing something because 4294967295 is 
greater than 1000. So, we exclude daemons because user activity is the prime 
target.

-Steve

RE: Why exclude unset auid in STIG rules

[Wyatt, Curtis]

Ok, so the assumption is that daemons are not compromised?  In other words, if a daemon is compromised (or could be compromised), wouldn't you want to monitor it's behavior as well?


-----Original Message-----
From: Steve Grubb [mailto:sgrubb@redhat.com] 
Sent: Wednesday, May 11, 2016 11:35 AM

When a user logs in, the auid gets set to the uid that they used to login with. Daemons are not user sessions and have the loginuid set to  -1. The auid representation is an unsigned 32 bit integer. So, -1 becomes 4294967295. The rules use a directive like this: -F auid>=1000 to trigger on user activity. It turns out that would trigger on daemons doing something because 4294967295 is greater than 1000. So, we exclude daemons because user activity is the prime target.

Re: Why exclude unset auid in STIG rules

[Steve Grubb]

On Wednesday, May 11, 2016 06:40:52 PM Wyatt, Curtis wrote:
> Ok, so the assumption is that daemons are not compromised?

This is a complicated topic. Basically there are different levels of paranoia. 
The STIG in my mind addresses basic robustness. If you read through the SRG, 
the things its requiring are reasonable but not paranoid.

I also think of it as a starting point. You can certainly tighten your system 
more than the STIG calls out. This is because you have specific knowledge of 
your operating environment and the threats that go with it. This might be for 
example knowledge about a daemon you have installed and whether or not its 
likely to be compromised. You can, with specific knowledge, add rules just for  
that daemon. But I don't think everyone wants to be held to the needs of a 
particular setup.

I think there is a difference in what rules you would use to spot bad user 
activity vs the rules you would use for intrusion detection. (I am working on 
and testing rules for intrusion detection and they will be in an upcoming 
release.)


> In other words, if a daemon is compromised (or could be compromised),
> wouldn't you want to monitor it's behavior as well?

Perhaps if you feel that this is likely to happen in your environment. You may 
also wind up with so many events that you cannot see what a rogue employee 
just did right before they quit. Or so many events that you only can keep the 
last hour's logs on-hand.

I don't see anything in the SRG that leans towards IDS-like rules. Do you see 
any?

-Steve

> -----Original Message-----
> From: Steve Grubb [mailto:sgrubb@redhat.com]
> Sent: Wednesday, May 11, 2016 11:35 AM
> 
> When a user logs in, the auid gets set to the uid that they used to login
> with. Daemons are not user sessions and have the loginuid set to  -1. The
> auid representation is an unsigned 32 bit integer. So, -1 becomes
> 4294967295. The rules use a directive like this: -F auid>=1000 to trigger
> on user activity. It turns out that would trigger on daemons doing
> something because 4294967295 is greater than 1000. So, we exclude daemons
> because user activity is the prime target.

RE: Why exclude unset auid in STIG rules

[Wyatt, Curtis]

> -----Original Message-----
> From: Steve Grubb [mailto:sgrubb@redhat.com]
> Sent: Wednesday, May 11, 2016 12:11 PM
> 
> On Wednesday, May 11, 2016 06:40:52 PM Wyatt, Curtis wrote:
> > Ok, so the assumption is that daemons are not compromised?
> 
> This is a complicated topic. Basically there are different levels of paranoia.
> The STIG in my mind addresses basic robustness. If you read through the
> SRG, the things its requiring are reasonable but not paranoid.
> 
> I also think of it as a starting point. You can certainly tighten your system
> more than the STIG calls out. This is because you have specific knowledge of
> your operating environment and the threats that go with it. This might be for
> example knowledge about a daemon you have installed and whether or not
> its likely to be compromised. You can, with specific knowledge, add rules just
> for that daemon. But I don't think everyone wants to be held to the needs of
> a particular setup.

That makes sense, because the STIGS are applied to a wide variety of systems
operating in a variety of threat environments.

> 
> I think there is a difference in what rules you would use to spot bad user
> activity vs the rules you would use for intrusion detection. (I am working on
> and testing rules for intrusion detection and they will be in an upcoming
> release.)

Love this.

> > In other words, if a daemon is compromised (or could be compromised),
> > wouldn't you want to monitor it's behavior as well?
> 
> Perhaps if you feel that this is likely to happen in your environment. You may
> also wind up with so many events that you cannot see what a rogue
> employee just did right before they quit. Or so many events that you only
> can keep the last hour's logs on-hand.

Which is why I'm also exploring the best options for compressing logs.  But
that's another topic for another time.

> 
> I don't see anything in the SRG that leans towards IDS-like rules. Do you see
> any?

No, I do not.  But now I understand all the reasoning. 
As always, your very helpful, thanks.

Curtis

Re: Why exclude unset auid in STIG rules

[Warron S French]

This is an interesting development.  I will have to keep my eyes peeled for this thread.

Warron French, MBA, SCSA

________________________________________
From: linux-audit-bounces@redhat.com <linux-audit-bounces@redhat.com> on behalf of Wyatt, Curtis <Curtis.Wyatt@gd-ms.com>
Sent: Wednesday, May 11, 2016 4:16 PM
To: Steve Grubb
Cc: linux-audit@redhat.com
Subject: RE: Why exclude unset auid in STIG rules

> -----Original Message-----
> From: Steve Grubb [mailto:sgrubb@redhat.com]
> Sent: Wednesday, May 11, 2016 12:11 PM
>
> On Wednesday, May 11, 2016 06:40:52 PM Wyatt, Curtis wrote:
> > Ok, so the assumption is that daemons are not compromised?
>
> This is a complicated topic. Basically there are different levels of paranoia.
> The STIG in my mind addresses basic robustness. If you read through the
> SRG, the things its requiring are reasonable but not paranoid.
>
> I also think of it as a starting point. You can certainly tighten your system
> more than the STIG calls out. This is because you have specific knowledge of
> your operating environment and the threats that go with it. This might be for
> example knowledge about a daemon you have installed and whether or not
> its likely to be compromised. You can, with specific knowledge, add rules just
> for that daemon. But I don't think everyone wants to be held to the needs of
> a particular setup.

That makes sense, because the STIGS are applied to a wide variety of systems
operating in a variety of threat environments.

>
> I think there is a difference in what rules you would use to spot bad user
> activity vs the rules you would use for intrusion detection. (I am working on
> and testing rules for intrusion detection and they will be in an upcoming
> release.)

Love this.

> > In other words, if a daemon is compromised (or could be compromised),
> > wouldn't you want to monitor it's behavior as well?
>
> Perhaps if you feel that this is likely to happen in your environment. You may
> also wind up with so many events that you cannot see what a rogue
> employee just did right before they quit. Or so many events that you only
> can keep the last hour's logs on-hand.

Which is why I'm also exploring the best options for compressing logs.  But
that's another topic for another time.

>
> I don't see anything in the SRG that leans towards IDS-like rules. Do you see
> any?

No, I do not.  But now I understand all the reasoning.
As always, your very helpful, thanks.

Curtis

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Why exclude unset auid in STIG rules

[Wyatt, Curtis]

I don't understand why the STIG audit rules have -F auid!=4294967295 in it.  If auid is unset, why wouldn't you still want to see the events in the logs?

Curtis