Fedora21 – Quick and Dirty with Firewalld

firewall

Hey, are you new to Firewalld like most of us?

Unless you have been using Firewalld in the last few releases of Fedora, as some out there have, then you probably could probably use a few pointers to get you started on your way to configuring your Linux firewalls the “new-fangled fancy way”. This is especially the case if you plan on moving to RHEL7 anytime soon — as Firewalld is the default there. So put on your big boy (or girl) pants and say goodbye to your old friend IPTABLES.

According to this page. Firewalld is…

“The dynamic firewall daemon firewalld provides a dynamically managed firewall with support for network zones to assign a level of trust to a network and its associated connections and interfaces. It has support for IPv4 and IPv6 firewall settings. It supports Ethernet bridges and has a separation of runtime and permanent configuration options. It also has an interface for services or applications to add firewall rules directly”

Wow, how fancy. So how do we use it? Well let’s take a stab at enabling HTTP access to our Fedora21 workstation.

First thing first, lets figure out what our default done is on our workstation.

$ sudo firewall-cmd –get-default-zone
FedoraWorkstation

Ok, thats a bit strange, in RHEL you should expect PUBLIC to be your default zone.  Now that we know what zone we need to mess with let’s make sure that its applied to the proper interfaces.

$ sudo firewall-cmd –get-active-zone
FedoraWorkstation
interfaces: enp4s0 enp5s4 macvtap0 tun0 virbr0

The first two interfaces above are our physical interfaces, so we are good here. Now lets apply the rule, and make sure its permanent.

$ sudo firewall-cmd –permanent –zone=FedoraWorkstation –add-service http
success

Now lets check our rules. Note HTTP is missing.

$ sudo firewall-cmd –list-services
dhcpv6-client mdns samba-client ssh

Since we have only applied this new rule to our permanent config and not to our running config, we need to restart firewalld to see the updated rule.

 $ sudo firewall-cmd –reload

Now your can view the updated rules…

$ sudo firewall-cmd –list-services
dhcpv6-client http mdns samba-client ssh

Insync: The Powerful Google Drive Client For Linux

Insync

Insync is a very powerful and full featured Google Drive client for Windows, Mac, and Linux. I ran across Insync when I was looking for a Google Drive client for Linux after I kicked Dropbox to the curb and switching over to Google Drive for all my cloud storage needs.

In all honestly, if it wasn’t for the Insync client I do not think that I would have made the switch at all, as Google does not even offer a basic GUI client for Linux. Really Google?

PSA: The integration that Google Drive provides into Google Photos, Google Music, Google Docs, and Gmail is well worth the switch from Dropbox in my opinion, and 1TB for only 9 bucks a month is hard to beat (100GB is only $1.99 a month). Just having a Gmail account gives you access to 15GB of free space… so there is no reason not to give it a try.

Ok now back to the topic at hand.

Note that a personal license of the Insync Google Drive client is not free, rather it costs $15. However you can download and try it risk free and without entering any credit card info. This one time fee for a personal license allows you to run and install Insync on multiple machines. Currently I have it installed on 4 separate Linux workstations/laptops. Its well worth cash.

Installing Insync is very easy and well documented so I am not going to go into that topic here. Rather lets talk about using Insync on Linux.

Continue reading

RHEL6: Cool PAM Tricks – Logging Terminal Keystokes

Pam-original-cooking-spray-72450This is a neat and very useful trick that I learned today. Lets say that you want to be able to monitor and log all keystrokes that are typed as root. This is particularly useful as normally you can only log when a user uses sudo to run a command. If the user has the abilty to become root however,  then they have effectively eluded yourattempts to track their activity. Like Thomas Magnum shaking a tail, they are free to scoot around your island with the top down.

So how do you stop this from occuring? How to you log all activity and keystrokes made by root without implementing a bloated 3rd party software that will probably cost and arm and a leg? You use PAM you dingbat.
 

The secret sauce in this security burrito is the pam_tty_audit.so module. Here is how to use it,

Below is my stock /etc/pam.d/system-auth file

#%PAM-1.0
# This file is auto-generated.
# User changes will be destroyed the next time authconfig is run.
auth        required      pam_env.so
auth        sufficient    pam_fprintd.so
auth        sufficient    pam_unix.so nullok try_first_pass
auth        requisite     pam_succeed_if.so uid >= 500 quiet
auth        required      pam_deny.so

account     required      pam_unix.so
account     sufficient    pam_localuser.so
account     sufficient    pam_succeed_if.so uid < 500 quiet
account     required      pam_permit.so

password    requisite     pam_cracklib.so try_first_pass retry=3 type=
password    sufficient    pam_unix.so md5 shadow nullok try_first_pass use_authtok
password    required      pam_deny.so

session     optional      pam_keyinit.so revoke
session     required      pam_limits.so
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
session     required      pam_unix.so

Now look above and then look below at my modified system-auth file. Note the additonal session entry for pam_tty_audit.so.

[root@ip-172-31-21-28 pam.d]# cat system-auth
#%PAM-1.0
# This file is auto-generated.
# User changes will be destroyed the next time authconfig is run.
auth        required      pam_env.so
auth        sufficient    pam_fprintd.so
auth        sufficient    pam_unix.so nullok try_first_pass
auth        requisite     pam_succeed_if.so uid >= 500 quiet
auth        required      pam_deny.so

account     required      pam_unix.so
account     sufficient    pam_localuser.so
account     sufficient    pam_succeed_if.so uid < 500 quiet
account     required      pam_permit.so

password    requisite     pam_cracklib.so try_first_pass retry=3 type=
password    sufficient    pam_unix.so md5 shadow nullok try_first_pass use_authtok
password    required      pam_deny.so

session     optional      pam_keyinit.so revoke
session     required      pam_tty_audit.so enable=root
session     required      pam_limits.so
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
session     required      pam_unix.so

Note that you will need to add the pam_tty_audit.so call to your /etc/pam.d/password-auth as well to ensure that you capture all of root's keystrokes, no matter how they log in.

 

Related articles

Much Todo About Linux/RHEL Passwords
RHEL6 – How to Manually Logout of an Iscsi Disk
Fun With PAM: Working with pam_cracklib and pam_tally2

Password Protecting Grub in RHEL 6

19552780-illustration-of-cartoon-wormGrub, is the standard boot loader used by each and every Linux type operating system that I can think of. RHEL 6 uses what I guess we are now calling grub 1.o, since grub 2.0 has been released and in use by Fedora for the last few releases. You will also find that grub 2.0 has replaced grub 1.0 in RHEL 7. At some point I plan to explore grub 2 at lenght, but today is not that day (unless something strange happens before I go to bed tonight — you never know).

 

Anyway – I digress. Below is an excerpt from the current grub.conf that is in use by my EC2 RHEL 6.5 instance. I've made it really tiny to save space.

# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE:  You do not have a /boot partition.  This means that
#          all kernel and initrd paths are relative to /, eg.
#          root (hd0)
#          kernel /boot/vmlinuz-version console=ttyS0 ro root=/dev/vda1
#          initrd /boot/initrd-[generic-]version.img
#boot=/dev/vda
default=0
timeout=1

splashimage=(hd0)/boot/grub/splash.xpm.gz

hiddenmenu
title Red Hat Enterprise Linux Server (2.6.32-431.17.1.el6.x86_64)
        root (hd0)
        kernel /boot/vmlinuz-2.6.32-431.17.1.el6.x86_64 console=ttyS0 ro root=UUID=05e7b919-2577-40a7-91fb-1ccdede87fc4 rd_NO_LUKS  KEYBOARDTYPE=pc KEYTABLE=us LANG=en_US.UTF-8 xen_blkfront.sda_is_xvda=1 console=ttyS0,115200n8 console=tty0 rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=auto rd_NO_LVM rd_NO_DM rhgb quiet
        initrd /boot/initramfs-2.6.32-431.17.1.el6.x86_64.img

To configure a password to use for grub you need to use the grub-crypt command. as you can see in the example below, grub-crypt prompts you for your password, although you can also pass the password to grub-crypt in the inital command. Grub-crypt spits out your hashed and salted password.

[root@ip-172-31-22-45 ~]# grub-crypt
Password:
Retype password:
$6$V0qkcD4b/CouCY/L$.7vrHd.X6MZWzzDxvXdQn3avPwv2rUX80XKuS.Hvh1YqR11ZyINZszvJ/e0qH6VcsFMAVWAPWXtugHHYTzYj90

Now stick this password in your grub.conf using the format below.

password –encrypted $6$V0qkcD4b/CouCY/L$.7vrHd.X6MZWzzDxvXdQn3avPwv2rUX80XKuS.Hvh1YqR11ZyINZszvJ/e0qH6VcsFMAVWAPWXtugHHYTzYj90

You have a couple of options when inserting the password into the grub.conf. You can either stick this entry near the top of the file, which protects each and every boot image that you might be configured to use, or you can stick the entry directly into a particular stanza to protect a specific boot image. For example, if you are building your servers with the option to pxe-boot from grub, or wipe the disk from grub, you might want to protect these options with a password.

Also note that adding a password to grub does not keep an unauthorized user from being able to boot or reboot a server, rather what it does is protect the grub menu from being edited manually durring a reboot. This keeps nefarious users from being able to break the boot sequence and boot into single-user mode where they can compromise your system.

 

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Fun With PAM: Working with pam_cracklib and pam_tally2

Liberty-bell_13850_smPlugable Authentication Modules, or PAM, is the standard mechanism that most Unix and Linux Operatng Systems use for user credential authentication. By design, PAM is broken out into a number of files, each with a specific purpose. Before you can get started with PAM you need to understand a bit about how PAM configuration files are formatted.  So lets get into that first before we try to bite off anything more.

 

PAM Config File Standards:

PAM config files follow a standard format as shown below.

Rule Types        Control        Module [module arguments]

 

There are 4 Rule Types

  • auth – used to authenticate users/passwords
  • account – set properties for a user's account
  • password – controls password changes
  • session – sets and controls environmental variables

And there are 5 Control Types

  • required – a module that a user is required to pass
  • sufficient – a user is not required to pass a sufficient module
  • optional – these modules do not have to be passed sucessfully
  • include – these rules reference other PAM config files
  • requisite – similar to required, but if failed, no further rules are checked

 

Configuring pam_cracklib:

Pam_cracklib is used to define password complexity. It has several module arguments that can be used to define password complexity and lenght. Its most common arguments are show below

  • ucredit – when used in the following format (ucredit=-n) requires the defined number of uppercase characters in a password
  • dcredit – when used in the following format (dcredit=-n) requires the defined number of digits in a password
  • ocredit – when used in the following format (ocredit=-n) requires the defined number of other (think symbols) type charaters in a password
  • lcredit – when used in the following format (lcredit=-n) requires the defined number of lower case letters  in a password
  • minclass – defines the minimum number of different character classes that must be present in a password.
  • minlen – defines the minimum required lenght of a password.

Here's a usage example of the cracklib module from a /etc/pam.d/system-auth file. In this example try_first_pass tells pam to try to use any cached credentials, while retry allows a user to try their password 3 times before the fail this module.

password    requisite     pam_cracklib.so minlen=8 ocredit=-1 ucredit=-1 try_first_pass retry=3

 

Configuring pam_tally2:

Pam_tally2 can be used to lock users after a defined number of failed login attempts. The example below, taken from the system-auth file will lock a user after 3 failed login attempts, will automatically unlock the user after 300 seconds, and will do so quietly, without any notification to the user.

auth        required        pam_tally2.so deny=3 unlock_time=300 quiet

The command pam_tally2 can be used to list users with failed logins and can also be used to reset a user's failed login count. See reset example below

pam_tally2 –reset –u testuser

Note that pam_tally2 deprecates the faillock module.

 

Supplementary PAM Configuration Options:

Want to limit a user to a particular number of concurrent ssh sessions? You can set this up in /etc/security/limits.conf if you are calling the pam_limits.so in your pam configs. Limits.conf provides the example below. Just copy the format and you are off to the races. Remember to remove the #.

#@student        -       maxlogins       4

 

 

Related articles

How to enforce password complexity on Linux
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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

Summary:
  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

Summary:
  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:
—-
user::rw-
group::r–
other::r–
—-
                  D: <NONE>
            new = A:
—-
user::rwx
group::rwx
other::rwx
—-
                  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.

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Finding Files with Special Permissions in Linux

Special-k-diet-1Ok, before you even attempt to read this post, I am assuming that you not only understand standard UNIX file permissions, but that you also understand special file permissions. What are special file permissions you ask. Well you know them as setuid, setgid, and the stickbit. If you don’t know what these things are then I will give you a very brief introduction.

Setuid – when set on a file, runs a command as root, a good example of this is the password command as shown below.

[root@localhost ~]# ls -l /usr/bin/passwd
-rwsr-xr-x. 1 root root 27156 Aug  3  2013 /usr/bin/passwd

Setgid – when set on a file, elevates permissions to the group ownership of a file. When set on a directory, causes all files created in that directory to be inherit group ownership from the directory.

Sticky Bit – when set on a directory, blocks a user from renaming or removing a file that they do not own.

Now lets use the find command to find files on our linux box with special permissions.

To match a special permission with a specific octal number specify the octal number as shown below. Note that this command does not return anything at all as there are no files on my system with the perms 4000.

[root@localhost ~]# find / -perm 4000

To match the permissions on a file using a specific prefix use the ‘-‘ switch as shown below. Its basically a wildcard search, which searches on the fields that you specified.

[root@ip-172-31-22-45 ~]# find /bin -perm -4000 | head -n 5
/bin/umount
/bin/mount
/bin/ping
/bin/su
/bin/ping6

As shown below, this command returns us all files in the /bin directory with the setuid bit set. In octal 4 is setuid.

[root@ip-172-31-22-45 ~]# ls -l /bin/ping
-rwsr-xr-x. 1 root root 40760 Sep 17  2013 /bin/ping

The next example returns us all files in /bin with the setgid bit set. Note that the octal value of the setgid bit is 2.

[root@ip-172-31-22-45 ~]# find /bin -perm /2000 | head -n 3
/bin/cgexec
/bin/cgclassify

See I told you so…

[root@ip-172-31-22-45 ~]# ls -l /bin/cgexec
-rwxr-sr-x. 1 root cgred 16384 Dec  2  2013 /bin/cgexec

Now lets get silly and try to match two octal values at once. This time we are going to search for files where both the setuid and setgid bits are set. As we know 4 + 2 = 6, so our command is as shown below

[root@ip-172-31-22-45 ~]# find /bin -perm -6000 | head -n 3

Note that this command does not return anything at all. However if we modify it a bit so that it searches for files that either have the setuid or the setgid bit set. To do this we use the ‘/’ modifier as shown below in my awesome example.

[root@ip-172-31-22-45 ~]# find /bin -perm /6000 | xargs ls -l
-rwxr-sr-x. 1 root cgred 16352 Dec  2  2013 /bin/cgclassify
-rwxr-sr-x. 1 root cgred 16384 Dec  2  2013 /bin/cgexec
-rwsr-xr-x. 1 root root  77336 Apr 10 04:50 /bin/mount
-rwsr-xr-x. 1 root root  40760 Sep 17  2013 /bin/ping
-rwsr-xr-x. 1 root root  36488 Sep 17  2013 /bin/ping6
-rwsr-xr-x. 1 root root  34904 Mar  5 07:21 /bin/su
-rwsr-xr-x. 1 root root  53472 Apr 10 04:50 /bin/umount

In this example below I am searching for files that either have the setuid (4), the setgid (2), or the stickybit (1) set.

[root@ip-172-31-22-45 ~]# find /bin -perm /7000 | xargs ls -l
-rwxr-sr-x. 1 root cgred 16352 Dec  2  2013 /bin/cgclassify
-rwxr-sr-x. 1 root cgred 16384 Dec  2  2013 /bin/cgexec
-rwsr-xr-x. 1 root root  77336 Apr 10 04:50 /bin/mount
-rwsr-xr-x. 1 root root  40760 Sep 17  2013 /bin/ping
-rwsr-xr-x. 1 root root  36488 Sep 17  2013 /bin/ping6
-rwsr-xr-x. 1 root root  34904 Mar  5 07:21 /bin/su
-rwsr-xr-x. 1 root root  53472 Apr 10 04:50 /bin/umount

To review. when using find if you do not specify any switches or options when searching for files by permissions, then you are attempting to do a specific match for files with those exact permissions. When you use the ‘-‘ option you are searching for files that match on a specific field. When you use the ‘/’ switch you are basically doing a wild card logical OR search. Use this option when you are searching for more than one type of special permission.

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