SSL Chain

I’ve ordered via a simple SSL-certificate signed by Comodo for use with apache… although a lot of browsers (Firefox on Mac OS X, all browsers in Linux) didn’t accepted it (CA was not know…)
After some discussion with …

Block mail from certain countries with sendmail

If you have your own MTA running… you are probably known with the spam-problems… Once you’ve tuned the filters, you have to do it again… because a new spam-run comes in. I also blocked whole /8 subnets in different countries (India/China/…)… but that is not a “real” solution… aka I want to block the whole country…

 The “DNSBL”  allows you to do so… the map ip-adresses to countries based on whois-information… so on my MTAs I added the following lines to the mc sendmail file:

FEATURE(dnsbl,`', `554 - Rejected - SPAM from Brazil:$&{client_addr} rejected')dnl
FEATURE(dnsbl,`', `554 - Rejected - SPAM from India:$&{client_addr} rejected')dnl
FEATURE(dnsbl,`', `554 - Rejected - SPAM from Korea:$&{client_addr} rejected')dnl
FEATURE(dnsbl,`', `554 - Rejected - SPAM from China:$&{client_addr} rejected')dnl
FEATURE(dnsbl,`', `554 - Rejected - SPAM from Romenia:$&{client_addr} rejected')dnl
FEATURE(dnsbl,`', `554 - Rejected - SPAM from Colombia:$&{client_addr} rejected')dnl
FEATURE(dnsbl,`', `554 - Rejected - SPAM from Macedonia:$&{client_addr} rejected')dnl
FEATURE(dnsbl,`', `554 - Rejected - SPAM from Vietnam:$&{client_addr} rejected')dnl
FEATURE(dnsbl,`', `554 - Rejected - SPAM from Russia:$&{client_addr} rejected')dnl

And within a few hours the first are already blocked… I hope this will reduce the amount of incomming spam at the “front door”. Because simply… I don’t know people in these countries…

CentOS 5 enabling Two-factor SSH authentication via Google

Today I noticed a very nice article about enabling Google’s two-factor authentication for Linux SSH.

After reading it… I found some time to play with it… so I enabled it within 10 minutes on my CentOS 5 64bit play-ground server… but there are some small ‘caveats’.

hg – Command

To checkout the code, you must make install the mercurial RPM… this one is available via the EPEL repositories.

So after having the EPEL repositories enabled, run as root:

yum -y install mercurial

Compiling the PAM module

When you checked out the code.

hg clone google-authenticator/

You cannot compile directly the module… therefor you must apply a small change to the Makefile.

Change where /usr/lib/ is stated to /usr/lib64/ (3 occurrences)

$ make
$ sudo make install

Now you’ve to update the /etc/pam.d/sshd so it contains:

auth       required
auth       include      system-auth
account    required
account    include      system-auth
password   include      system-auth
session    optional force revoke
session    include      system-auth
session    required

Configure SSH

You also have to make sure that in /etc/ssh/sshd_config the following settings are set on yes:

ChallengeResponseAuthentication yes
UsePAM yes

And restart the SSH-daemon

Set up your smartphone/credentials on the system

$ google-authenticator×200&chld=M|0&cht=qr&chl=otpauth://totp/[email protected]%3Fsecret%3DSAEP64T5VZAVWAFB
Your new secret key is: SAEP64T5VZAVWAFB
Your verification code is 376046
Your emergency scratch codes are:
Do you want me to update your “~/.google_authenticator” file (y/n) y
Do you want to disallow multiple uses of the same authentication
token? This restricts you to one login about every 30s, but it increases
your chances to notice or even prevent man-in-the-middle attacks (y/n) y
By default, tokens are good for 30 seconds and in order to compensate for
possible time-skew between the client and the server, we allow an extra
token before and after the current time. If you experience problems with poor
time synchronization, you can increase the window from its default
size of 1:30min to about 4min. Do you want to do so (y/n) n
If the computer that you are logging into isn’t hardened against brute-force
login attempts, you can enable rate-limiting for the authentication module.
By default, this limits attackers to no more than 3 login attempts every 30s.
Do you want to enable rate-limiting (y/n) y

And you’re done :-D

Give it a try to SSH to that box…

 TIP: Make sure you’ve an SSH session still open… or you might lock yourself out of the system…

Creating Snapshots of a backup using LVM snapshot

Normally I used to have a backup-retention-script in place that will create a TAR-ball of the backup data (using Herakles). But this way I was not able to have a retention of longer then 3 days :-(

So I had to look into another solution, I could add a new harddrive in the server… but there should be something else possible. So I ended up by using LVM snapshots. So I created a Volume group of about 100GB. In that volume group I created a logical volume of about 30GB, which is enough (and if not, we can ‘grow’ the Filesystem thanks to LVM :-) )

After having all that done, I’ve created a script located in /root/scripts/lvm-snapshot. This script runs every midnight and creates a snapshot.

# Create LVM Snapshots
CURRENT_SNAPNAME=”snap-“$(date “+%Y%m%d%H%M%S”)

echo $LINE
df -h /mnt/data
echo $LINE
$LVMSNAPSHOTCMD 2> /dev/null
CURRENT_SNAPSHOT_COUNT=$(lvdisplay | grep “^  LV Name                /dev/vol_backup/snap” | sort | awk ‘{ print $3 }’ | wc -l)

if [ $OVERFLOW -gt 0 ];
        echo $LINE
        for files in  $(lvdisplay | grep “^  LV Name                /dev/vol_backup/snap” | sort | awk ‘{ print $3 }’ | head -n$OVERFLOW);
                 /usr/sbin/lvremove -f $files 2> /dev/null
echo $LINE
/usr/sbin/vgdisplay vol_backup
echo $LINE
/usr/sbin/lvdisplay $VOLUME2SNAPSHOT

And the crontab entry is:

# crontab -l
0 0 * /root/scripts/lvm-snapshot

Require client-SSL certificate for certain content.

On a kind of “intranet” website, which is secured with username/password combinations and HTTPS I’ve implemented the next feature:

– Authorized users can read everything on the website

– Files with in their filename “classified” requires a valid SSL-Client certificate…

Here is the output of my apache config:

<Directory /usr/sites/ssl-site/intranet/htdocs>
  Options Indexes MultiViews
  AllowOverride Authconfig
  Order allow,deny
  Allow from all
  AuthName “intranet”
  AuthType “Basic”
  AuthUserFile /usr/sites/ssl-site/intranet/etc/users.pwl
  require valid-user

<LocationMatch .*(c|C)(l|L)(a|A)(s|S)(s|S)(i|I)(f|F)(i|I)(e|E)(d|D).+>
  SSLVerifyClient require
  SSLVerifyDepth 1
  SSLOptions +OptRenegotiate


I still have to sort out some issues, like directories having a directory with the name “classified” in them.