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

How to mount dd images under Linux

For a raw filesystem try:

fdisk -l harddrive.img
mount -o ro,loop,offset=xxxxxxxxx harddrive.img /mnt/loop

or for filesystems with volume groups etc try:

losetup /dev/loop0 disk.img
kpartx -a /dev/loop0

Then to mount the first partition:

mount /dev/mapper/loop0p1 /mnt

Or to activate the volume group then mount the logical volume:

vgscan
vgchange -ay vg
mount /dev/vg/lv /mnt

Hope that helps.

Enable Apache’s inbuilt chroot functionality

This works on all versions of Apache webserver greater than 2.2.10.
I’ll presume you have a current working version of Apache serving files from /var/www/

mkdir -p /chroot/var/ 

Required for PHP5 compatibility:

mkdir -p /chroot/var/lib/php5
chown root:www-data /chroot/var/lib/php5
chmod 770 /chroot/var/lib/php5
cp /etc/localtime /chroot/etc/localtime
cp -R /usr/share/zoneinfo /chroot/usr/share/zoneinfo
cp -R /usr/share/apache2 /chroot/usr/share/apache2 
mv /var/www /chroot/var/ 

To help with compatibility and user / sysadmin expectations

ln -s /chroot/var/www /var/www 

Enable Apache’s in-built chroot (Debian)

echo "ChrootDir /chroot" > /etc/apache2/conf.d/chroot 

Enable Apache’s in-built chroot (Redhat/CentOS/Fedora)

echo "ChrootDir /chroot" >> /etc/httpd/conf/httpd.conf 
semanage fcontext -a -t httpd_sys_content_t “/chroot/var/www(/.*)?”
service apache2 restart 

Now test your damn website! Logfiles are your friend for troubleshooting any bugs :-)

How to measure IOPS with linux

So many times I need to measure the amount of IOPS on a Linux disk/storage system. While there are many tools for the jobs they just don’t seem to give you a ‘number’. For example Splunk indexers require 1200+ IOPS according to hardware recommendation guides but how do you find out if your any where close to that number? Use ‘bonnie++’, ‘iozone’ or perhaps ‘fio’? Well use any of those tools will create the type of read / write sequence you would like to replicate - but where the damn magic number???

Easiest two ways are:
Method #1:
run iozone -a (or bonnie++) in one screen then in another session / terminal use nmon, pressing D (capital D) to get disk stats and get the number from the Xfers column. This is your magic number (or IOPS reading)

┌nmon─14i─────────────────────Hostname=reddragon─────Refresh= 2secs ───19:51.57─
│ Disk I/O ──/proc/diskstats────mostly in KB/s─────Warning:contains duplicates─
│DiskName Busy    Read    Write       Xfers   Size  Peak%  Peak-RW    InFlight
│sda       99%    699.9     14.0KB/s  178.0   4.0KB  493%    3658.8KB/s   1   
│sda1       0%      0.0      0.0KB/s    0.0   0.0KB    0%       0.0KB/s   0   
│sda2      99%    699.9     14.0KB/s  178.0   4.0KB  493%    3658.8KB/s   1   
│dm-0       0%      0.0      0.0KB/s    0.0   0.0KB    0%       0.0KB/s   0   
│dm-1      99%    699.9     14.0KB/s  178.5   4.0KB  494%    3658.8KB/s   1   
│dm-2       0%      0.0      0.0KB/s    0.0   0.0KB   76%    2553.5KB/s   0   
│Totals Read-MB/s=2.1      Writes-MB/s=0.0      Transfers/sec=534.4 

In the above example I’m getting about 178 IOPS for my disk ’sda’

Method #2:
run fio with the correct workload (google how to use fio) and while it’s running it will actually tell you the IOPS.

[root@reddragon ~]# fio random-read-test.fio 
random-read: (g=0): rw=randread, bs=4K-4K/4K-4K/4K-4K, ioengine=sync, iodepth=1
fio-2.0.13
Starting 1 process
Jobs: 1 (f=1): [r] [85.1% done] [736K/0K/0K /s] [184 /0 /0  iops] [eta 00m:28s]

In this example I am getting 184 IOPS. Also if you wait until fio finishes it run - you can the IOPS reading from there. Eg.

random-read: (g=0): rw=randread, bs=4K-4K/4K-4K/4K-4K, ioengine=sync, iodepth=1
fio-2.0.13
Starting 1 process
Jobs: 1 (f=1): [r] [98.9% done] [2224K/0K/0K /s] [556 /0 /0  iops] [eta 00m:02s]
random-read: (groupid=0, jobs=1): err= 0: pid=7239: Tue Feb 25 16:49:16 2014
  read : io=131072KB, bw=747406 B/s, iops=182 , runt=179578msec
    clat (usec): min=107 , max=117530 , avg=5473.62, stdev=4112.08
     lat (usec): min=107 , max=117531 , avg=5473.93, stdev=4112.08
    clat percentiles (usec):
     |  1.00th=[  245],  5.00th=[  302], 10.00th=[  370], 20.00th=[ 2480],
<SNIP>

As you can see: iops=182 - pretty consistent with the other results!