sshd without-password vs prohibit-password

Upgrading a server from Debian 8 to Debian 9 - I noticed in /etc/ssh/sshd_config that ‘PermitRootLogin’ had the argument ‘prohibit-password’. Having not seen that before I wondered what the difference was between that and ‘without-password’.
Turns out that mean and do the same thing - but ‘prohibit-password’ was introduced to be less ambigous. So there you have it!

Check out the release notes here for proof :-)

Filter Ansible logs on CentOS 7

CentOS 7 and Redhat 7 seem to love shoving logs into /var/log/messages and if you run ansible in-house then it generates a lot of noise and if you run Splunk or ELK then getting your logs ‘just right’ is important to O.C.D type levels!

To send your ansible generated logs to /var/log/ansible.log perform the following:

Create the file /etc/rsyslog.d/ansible.conf

if ( $programname contains "ansible" ) then /var/log/ansible.log
& stop

and if you are creating log files you will want to manage those log files too!
Create the file /etc/logrotate.d/ansible

/var/log/ansible.log {
        notifempty
        weekly
        rotate 4
        missingok
        compress
    }

And restart / reload rsyslog

service rsyslog restart

Configure Centrify Express with Apache’s mod_auth_kerb

I was lucky enough to spend the morning trying to get mod_auth_kerb working with our existing installation of Centrify without creating any additional SPNs.

It was actually very straight forward except for the missing component of the secret sauce, that’s not documented in many places.
Basically to get it to work perform the following on RedHat 6 (and CentOS 6):

yum install httpd
yum install mod_auth_kerb

vim /etc/httpd/conf.d/auth_kerb.conf

#
# The mod_auth_kerb module implements Kerberos authentication over
# HTTP, following the "Negotiate" protocol.
#

LoadModule auth_kerb_module modules/mod_auth_kerb.so

#
# Sample configuration: Kerberos authentication must only be
# used over SSL to prevent replay attacks.  The keytab file
# configured must be readable only by the "apache" user, and
# must contain service keys for "HTTP/www.example.com", where
# "www.example.com" is the FQDN of this server.
#

<Location /private>
  SSLRequireSSL
  AuthType Kerberos
  AuthName "Kerberos Login"
  KrbMethodNegotiate On
  KrbMethodK5Passwd On
  KrbAuthRealms YOURDOMAIN.COM
  Krb5KeyTab /etc/krb5.keytab
# KrbServiceName is the Centrify secret sauce
  KrbServiceName http
  require valid-user
</Location>

chown root:apache /etc/krb5.keytab
chmod 640 /etc/krb5.keytab

And that’s it. Hopefully “KrbServiceName http” was the secret sauce you needed!

Add comments to IPTables firewall rules

Instead of just documenting the IPTables configuration file eg: /etc/sysconfig/iptables with comments (#’s) you can also input comments as part of the ruleset itself. So when you perform iptables -L -v -n you get the following output:

root@server070:[~]: iptables -L -v -n
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
  64M 4727M ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED
    5   474 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0
 202K   27M ACCEPT     all  --  lo     *       0.0.0.0/0            0.0.0.0/0
   16   880 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           state NEW tcp dpt:22
 137M   38G ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp dpt:514 /* Syslog traffic */
   28  1664 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:514 /* Syslog traffic */
41067 2050K ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:9997 /* Universal Forwarder traffic */
    0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:8089 /* Splunk SSL traffic */
   47  2564 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:8000 /* Splunk web interface */
14135 1313K LOG        all  --  *      *       0.0.0.0/0            0.0.0.0/0           limit: avg 5/min burst 5 LOG flags 0 level 7 prefix `iptables denied: '
 218K   21M REJECT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           reject-with icmp-host-prohibited

All that you need to do use the following example in your configuration file:

root@server070:[~]: cat /etc/sysconfig/iptables
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
-A INPUT -p udp -m udp --dport 514 -m comment --comment "Syslog traffic" -j ACCEPT
-A INPUT -p tcp -m tcp --dport 514 -m comment --comment "Syslog traffic" -j ACCEPT
-A INPUT -p tcp -m tcp --dport 9997 -m comment --comment "Universal Forwarder traffic" -j ACCEPT
-A INPUT -p tcp -m tcp --dport 8089 -m comment --comment "Splunk SSL traffic" -j ACCEPT
-A INPUT -p tcp -m tcp --dport 8000 -m comment --comment "Splunk web interface" -j ACCEPT
-A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables denied: " --log-level 7
-A INPUT -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -j REJECT --reject-with icmp-host-prohibited
COMMIT

Happy commenting!

How to block malicious VBA documents and spreadsheets with spam assassin or amavisd

Monitoring our net streams for SMTP traffic, I have a particular Splunk alert configured to alert when a spam campaign in underway. It’s quite interesting to see what tricks spammers try and how long some campaigns last.

Something that has caught my attention is the increased use of unsolicited “invoice” and “order” emails which get sent with .doc documents attached. Reviewing the documents nearly all of them contain malicious VB scripting usually set to auto run, which downloads and tries to execute binaries.

Now I have created a number of spam assassin rules to block these types of emails (invoices with .doc files attached) but it’s a cat and mouse game, and you can’t be too generic as you may block legitimate email. What I can block ruthlessly is documents and spreadsheets which contain autorun VB scripting.

Here is how to do it:

Create the following file on your amavisd server at the location “/usr/local/bin/detectvba.pl”

#!/usr/bin/perl -w
# technion@lolware.net
# Detects vba macros containing blacklisted strings.
# https://github.com/technion/maia_mailguard/blob/master/scripts/detectvba.pl
# Mods by www.cammckenzie.com
#
# Suggested amavisd/maiad.conf config:
# ['Detect-VBA',
#   '/usr/local/bin/detectvba.pl', "{}",
#      [0], qr/INFECTED/, qr/\bINFECTED (.+)\b/m ],
#
use strict;

my $sigtool = '/usr/bin/sigtool'; #Clamav sigtool path

if ($#ARGV != 0) {
    print "Please supply directory to scan\n";
    exit 0;
}

#Sanity check directory
my $dir = $ARGV[0];
if ($dir !~ /^[a-z0-9A-Z\/-]+$/) {
    print "Invalid directory passed\n";
    exit 0;
}

opendir DIR, $dir or die "Cannot open dir $dir: $!";
my @files = readdir DIR;

foreach my $file (@files) {
    next if $file =~ /^\.$/;
    next if $file =~ /^\.\.$/;
    my $scan = `$sigtool --vba="$dir/$file"`;
    if ($scan =~ /autoopen/i ) {
        print "Scanning $file: INFECTED VBA\n";
        exit 1;
    } else {
        print "Scanning $file: OK\n";
    }
}

closedir DIR;

exit 0;

Then in amavisd.conf (/etc/amavisd/amavisd.conf on CentOS) modify the section “@av_scanners” and insert as a primary scanner the following stanza:

['Detect-VBA',
   '/usr/loca/bin/detectvba.pl', "{}",
      [0], qr/INFECTED/, qr/\bINFECTED (.+)\b/m ],

Then after that just restart your amavisd service and you should see, it finds Detect-VBA as a primary scanner, test it by sending yourself a malicious macro document lol.

Download the raw howto here, so that special characters are intact as FlatPress has a habit of removing them….https://www.cammcken … assin-or-amavisd.txt