RHEL6: Using Advanced Log File Filtering in Rsyslog

100-8591So by default when you forward logs to a syslog/rsyslog server all the logs end up in the same file (ususally configured to go to the messages file). Sometimes one may prefer to forward logs from a particular server to a separate logfile. I know for a fact that my sometimes friends in our info-sec group prefers this setup.

While managing such a setup for more than a handful of hosts would probably be a nightmare, its not actaually hard to setup on the most basic level.

First create a custom filters.conf (or whatever you want to name it) in your /etc/rsyslog.d directory. Below is the file that I created.

[root@ip-172-31-21-28 rsyslog.d]# cat filters.conf
:fromhost, isequal, "ip-172-31-25-104.ec2.internal" /var/log/ip-172-31-25-104.ec2.internal/messages
:fromhost, isequal, "ip-172-31-25-104.ec2.internal" ~

Note that you will need to include two lines in your file for each host, one with the specific file/location that you want to send your filtered log messages, and a second line that directs rsyslog to discard any messages from the specified hosts once they have been logged to the specified locations. This keeps these messages from ending up in the messages file as well as the file defined in your filter file.


Related articles

RHEL6 – Introduction to IPtables, Part II
HomeLab: Basic Syslog Configuration on Cisco Catalyst Devices
RHEL6- Getting Up Close and Personal With Rsyslog

Disabling Ctrl+Alt+Delete in RHEL 6

Ctrl-Alt-Del-Cup-SetLet me start off by saying that I am not a fan of disabling ctrl+alt+delete, especially if you do not have physical access to a server. Sometimes the old three finger salute is the best and quickest method to reboot a locked and unresponsive Operating System. Regardless of this fact, some Info Sec folks think that disabling this functionality is a good idea for security. So for their sake, I will show you how to do it.

First ssh into your server and become root and change directory to what is shown below.

[root@ip-172-31-22-45 ~]# cd /etc/init

Now copy the file below exactly as I have illustrated. You do not want to try to modify the original file as it could be overwritten by Upstart.

[root@ip-172-31-22-45 init]# cp control-alt-delete.conf control-alt-delete.override

Now modify the line below and change it to run a command that will exit with an exit code of 0.

exec /sbin/shutdown -r now “Control-Alt-Delete pressed”

Something like /bin/true will work, although I am sure that you can come up with more creative ideas.

exec /bin/true

Now try ctrl+atl+delete, nothing should happen.

Introduction to AIDE – Advanced Intrusion Detection Environment

Wally_Gator_PhotoEver heard of AIDE, neither had I. Apparently its a simple intrusion detection application that can be used to monitor file changes.  It can be confired to monitor permission, ownership, timestamp, or content changes.

Lets install it. Its in the stock Redhat repos, so its a piece of cake to install via yum.


[root@localhost ~]# yum -y install aide

Once installed, you can tweak the config file (/etc/aide.conf) to your liking. The stock config is pretty robust, so I am going to trim it down a bit and just monitor /etc for permission changes, and /bin for what are defined as normal changes. Normal looks at file hashes to see if the files have been modified.

/bin    NORMAL
/etc    PERMS

Now lets start aide

[root@localhost ~]# aide –init

AIDE, version 0.15.1

### AIDE database at /var/lib/aide/aide.db.new.gz initialized.


Now this part is silly, we need to rename the database created above to the name that aide is configured to use.

[root@localhost ~]# cp /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gz


Now lets check for changes.

[root@localhost ~]# aide –check

AIDE, version 0.15.1

### All files match AIDE database. Looks okay!

Hey no changes. Now lets monkey with something and see if aide catches it. In this example we are creating a new file in /etc. As seen below aide catches the new file and reports on it.


[root@localhost ~]# touch /etc/aide.test.change
[root@localhost ~]# aide –check
AIDE 0.15.1 found differences between database and filesystem!!
Start timestamp: 2014-07-15 19:51:14

  Total number of files:        5054
  Added files:                  1
  Removed files:                0
  Changed files:                0

Added files:

added: /etc/aide.test.change


So now lets re-initialize the database, which is pretty much a snapshot.

[root@localhost ~]# aide –init

AIDE, version 0.15.1

### AIDE database at /var/lib/aide/aide.db.new.gz initialized.


Don't forget to overwrite the old database.

[root@localhost ~]# cp /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gz
cp: overwrite ‘/var/lib/aide/aide.db.gz’? yes

Now lets change the permissions on our test file and see if aide catches the change.  I'll spare you the suspense and let you know that aide did its job. See below.


[root@localhost ~]# chmod 777 /etc/aide.test.change
[root@localhost ~]# aide –check                    
AIDE 0.15.1 found differences between database and filesystem!!
Start timestamp: 2014-07-15 19:54:09

  Total number of files:        5054
  Added files:                  0
  Removed files:                0
  Changed files:                2

Changed files:

changed: /etc/aide.test.change
changed: /root/.mozilla/firefox/8u03e3hs.default/sessionstore.js

Detailed information about changes:

File: /etc/aide.test.change
 Perm     : -rw-r–r–                       , -rwxrwxrwx
 ACL      : old = A:
                  D: <NONE>
            new = A:
                  D: <NONE>

Now aide on its own is just a simple tool, but run via cron with a bit of tuning and a bit more logic behind it and I can see it being a very useful tool. Looking forward to playing with it more.

Related articles

How To Install Aide on a DigitalOcean VPS
RHEL6 – How to Setup an Anonymous Download Only FTP Server

Working With Extended Filesystem Attributes in Linux

GarfatIn my previous post I went over standard filesystem attibutes in Linux, and how to set and view those attibutes with lsattr and chattr. You can view that post here if you are interested.

In this post we are going to go over extended filesystem attibutes. Now there is not much to this as you are probably not going to ever have to use these settings. That being said, its not a bad thing to be aware of.

Attribute names are strings that can be set and configured at will using the setfatr command. They can be viewed with the getfattr command. There are 4 namespaces of attibutes, security, system, trusted, and user.

When using getfattr ( which I pronounce as getfatter) the -d option dumps only user namespace attibutes. The rest of the namespace attributes can be viewed by using the -m option along with the namespace name. In the example below you can see that there are no user namespace attibutes set on my anaconda-ks.cfg file, however there are attibutes set in the security namespace.

[root@localhost ~]# getfattr -d anaconda-ks.cfg
[root@localhost ~]# getfattr -d -m security anaconda-ks.cfg
# file: anaconda-ks.cfg


Using setfattr you can define and set custom attributes. See the useless example below.

[root@localhost ~]# setfattr -n user.example -v example anaconda-ks.cfg
[root@localhost ~]# getfattr -d anaconda-ks.cfg
# file: anaconda-ks.cfg

However this could be cool if you got an md5 sum on a file and dumped it into a file attibute. You could, in theory, use this process to see if someone has messed with one of your config files.


[root@localhost ~]# md5sum anaconda-ks.cfg
fda1aa550d3cf82423d1b1ad1ae53a13  anaconda-ks.cfg
[root@localhost ~]# setfattr -n user.md5sum -v fda1aa550d3cf82423d1b1ad1ae53a13 anaconda-ks.cfg
[root@localhost ~]# getfattr -d anaconda-ks.cfg
# file: anaconda-ks.cfg


Related articles

Why Extended Attributes are Coming to HDFS
Advanced Filesystem Attributes in Linux
How to create a file that root user also can't delete?

Yum: Under the Covers with GPG Keys

Skeleton_key_1_keychain_sculpture_photo_cut_outs-r558fef9b275d4609b522ac07970a6af6_x7sa6_8byvr_324Hey look at this spooky key. Don't be frightened little one. Nothing scary is going to happen to you here. This is a safe place. As a matter of fact, if you stick around you might just learn a thing or two. A thing or two about GPG!

First off do any of us really know what GPG stands for? Well yes we do! It stands for GNU Privacy Guard. RPM Package creators use GPG to apply a digital signature to their packages. If a package was tampered with, then its GPG signature will no longer match what was placed in the original package.

First off to check what keys you have installed on your Linux server you can run the following rpm command as show in the example below.

[root@ip-172-31-22-45 ~]# rpm -qa gpg-pubkey


Neet I have three keys installed. But lets say want to install another one. Well I can do so with the command below. In this example I have navigated to /etc/pki/rpm-gpg and am going to install the redhat beta key on my server.

[root@ip-172-31-22-45 rpm-gpg]# rpm –import RPM-GPG-KEY-redhat-beta

Hey that was fun. Now lets get our hands a bit dirtier.

Want to get more information on a specific key. Then this command is your huckleberry. Here you can see that this is the pubkey for the EPEL repo.

[root@ip-172-31-22-45 rpm-gpg]# rpm -qi gpg-pubkey-0608b895-4bd22942
Name        : gpg-pubkey                   Relocations: (not relocatable)
Version     : 0608b895                          Vendor: (none)
Release     : 4bd22942                      Build Date: Sat 14 Jun 2014 09:13:58 AM EDT
Install Date: Sat 14 Jun 2014 09:13:58 AM EDT      Build Host: localhost
Group       : Public Keys                   Source RPM: (none)
Size        : 0                                License: pubkey
Signature   : (none)
Summary     : gpg(EPEL (6) <epel@fedoraproject.org>)
Description :


To verify signature of a downloaded package, use the rpm command as shown below. In this example I have highlighted the key that was used to sign this package.

# rpm -vK nautilus-dropbox-1.6.0-1.fedora.i386.rpm
    Header V3 RSA/SHA1 Signature, key ID 5044912e: OK
    Header SHA1 digest: OK (a4d51906633f92913db075ba33946f50999c245e)
    V3 RSA/SHA1 Signature, key ID 5044912e: OK
    MD5 digest: OK (1b8ff7abc18f68bf274e24fc57fd3a87)


Using the bolded information in the example above, I can then use this information to track down the exact key that was used to sign the package.

[root@localhost Downloads]# rpm -qa | grep 5044912e


Is this awesome, well not really, but you never know when you might need to use this information. Like on a test. Wink Wink.

Related articles

Using Yum Update to Apply Security Patches Only
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Signing rpm packages with GPG

RPM Package Inspection for Fun and Profit

6a00d8341c562c53ef01538f8abd65970b-800wi"Whats in the box" — David Mills

Lets face it, one of your users needs to have a package installed on a system, you tend to do it for them. That is, as long as the package looks safe. Sure, your not going to install an rpm that is clearly dangerous, but as long as the package name looks reasonable and you trust the user, you might actually just go ahead an install it for them without thinking much about it. Hell, I know that I have done the exact same thing from time to time. And I have done it with an unsigned package.

"Sure you need this Oracle thing installed on this database server?"

 "You got it directly from Oracle right?"

But honestly, this is a very bad practice as you have no idea what the RPM is installing, and what its pre and post scripts might be doing to your system. Using the command below, you can inspect a packages post and pre install scripts to see if they are doing anything funny. In this instance I am taking a look at the dropbox package for my little Eeepc.

[root@localhost ~]# rpm -qp –scripts /root/Downloads/nautilus-dropbox-1.6.0-1.fedora.i386.rpm

If you have already installed a package and want to see what its pre and post install scripts did. You can run the command above using the installed package name. Note that you will drop the "P" from the command. See my sendmail example below.

[root@localhost ~]#rpm -q –scripts sendmail-8.14.8-2.fc20.i686


In addition to checking the pre and post scripts, you also want to check to see if the rpm has any triggers. What are triggers you ask? Well they are extensions to the normal install scripts, and they may often call for the installation of another package or the execution of a command. Just look at all the triggers that fire when you install sendmail.

[root@localhost ~]# rpm -q –triggers sendmail-8.14.8-2.fc20.i686
triggerun scriptlet (using /bin/sh) — sendmail < 8.14.5-3
/usr/bin/systemd-sysv-convert –save sendmail >/dev/null 2>&1 ||:
/bin/systemctl enable sendmail.service >/dev/null 2>&1
/bin/systemctl enable sm-client.service >/dev/null 2>&1
/sbin/chkconfig –del sendmail >/dev/null 2>&1 || :
/bin/systemctl try-restart sendmail.service >/dev/null 2>&1 || :
/bin/systemctl try-restart sm-client.service >/dev/null 2>&1 || :
# workaround for systemd rhbz#738022
/bin/systemctl is-active sendmail.service >/dev/null 2>&1 && \
        ! /bin/systemctl is-active sm-client.service >/dev/null 2>&1 && \
        /bin/systemctl start sm-client.service >/dev/null 2>&1 || :

Obviously you also want to check to see what files are actually part of a package. This can be accomplished with the query and list arguments seen below. Add the "P" argument if the rpm is not already installed. In this case I have already installed sendmail, so I exclude the "P" from the command.


[root@localhost ~]# rpm -ql sendmail-8.14.8-2.fc20.i686


So whats the moral of the story here. Well its really not that hard to take a minute and look under the covers and make sure that the packages that you are installing are not harming your systems. Is definetly worth 5 minutes of your time. Might just save your behind.


Related articles

RHEL6 – Simple Postfix Configuration
RHEL6 – Common Postfix Server Roles
Configure sendmail as a client for SMTPs
Sendmail Server

Quick and Dirty Yum Security Plugin Overview

Maneki-neko-mountain-tummy-13745890The YUM security plugin is a package that allows you to search specifically for security patches applicable to a Redhat/Centos server.  This functionality comes in very handy when having to cross reference CVEs to Redhat Security Advisories (RHSAs). If you work closely with anyone in an information security role, you already know how vital functionality is.

Before you can begin you need to make sure that you have the plugin installed.  Use the command below to install it.

# yum -y install yum-plugin-security


Then you can use the plugin to get a overview of the security updates availible for your system.

# yum updateinfo
Updates Information Summary: available
3 Security notice(s)
         1 Important Security notice(s)
         2 Moderate Security notice(s)
12 Bugfix notice(s)
1 Enhancement notice(s)


You can get a specific list of updates, sorted by security advisories, bug fixes, and enhancement advisories.

# yum updateinfo list


To get more specific information on a RHSA and the CVEs that it applies to, you can search by RHSA as seen below.

# yum updateinfo RHSA-2014:0771


Need to see what patches are required to address a certain CVE, then this next command is for you. Trust me this one is useful as it gives you a list of all required packages that address that CVE.

# yum updateinfo list –cve=CVE-2013-6378
Loaded plugins: amazon-id, rhui-lb, security
RHSA-2014:0771 Important/Sec. kernel-2.6.32-431.20.3.el6.x86_64
RHSA-2014:0771 Important/Sec. kernel-firmware-2.6.32-431.20.3.el6.noarch
RHSA-2014:0771 Important/Sec. kernel-headers-2.6.32-431.20.3.el6.x86_64
RHSA-2014:0771 Important/Sec. perf-2.6.32-431.20.3.el6.x86_64


Want to see a list of all fixes by severity. Then you can use the command below. Note that I am using important as my severity as there are no critical updates that are applicable to my test system at this time.

yum updateinfo list –sec-severity=Important
RHSA-2014:0771 Important/Sec. kernel-2.6.32-431.20.3.el6.x86_64
RHSA-2014:0771 Important/Sec. kernel-firmware-2.6.32-431.20.3.el6.noarch
RHSA-2014:0771 Important/Sec. kernel-headers-2.6.32-431.20.3.el6.x86_64
RHSA-2014:0771 Important/Sec. perf-2.6.32-431.20.3.el6.x86_64


You can also search for security fixes by package name as shown below.

# yum updateinfo list kernel
RHSA-2014:0771 Important/Sec. kernel-2.6.32-431.20.3.el6.x86_64


You can also use YUM to apply only security related updates. See below. This is useful if you are in a pinch and need to quickly apply all security updates to make your Infosec Team happy.

# yum –security update

Related articles

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