Help! SSH attack on Ubuntu 14.04.2 LTS – use sshdfilter with ufw

If you’ve got a *Nix machine on the public Internet, you will experience this at one time or another. If you run sshd on its’ known port 22, some script kiddie out there will attack it. With that, you’ll see that you’ll have a bunch of connections that probably and hopefully will never succeed. I saw these messages in my /var/log/auth.log:

Nov 15 06:44:26 chunli sshd[20634]: Failed password for root from port 41751 ssh2
Nov 15 06:44:26 chunli sshd[20636]: Failed password for root from port 41921 ssh2
Nov 15 06:44:26 chunli sshd[20638]: Failed password for root from port 42948 ssh2
Nov 15 06:44:26 chunli sshd[20546]: message repeated 2 times: [ Failed password for root from port 27586 ssh2]

I’ve experienced this before and to alleviate this problem, I used sshdfilter in the past. I know that there are others out there like sshblack that can do blacklisting of attackers or one of the easiest ways to alleviate this problem is just to run ‘sudo ufw limit ssh’. This is a way to block them from coming back for a while.

To get started, first stop SSH:

sudo initctl stop ssh

Then move /etc/init/ssh.conf out. We’ll start SSH with sshdfilter instead.

You’ll get a message in the auth.log here:
auth.log:Nov 16 19:54:36 chunli sshd[1150]: Missing privilege separation directory: /var/run/sshd

Because of this, we’ll just add a line in the /etc/init.d/sshdfilter file like this:

start() {
 echo -n $"Starting sshdfilter: "
 export PATH=$PATH:/usr/local/sbin
 mkdir /var/run/sshd
 return $RETVAL

In /etc/sshdfilterrc, I changed the chain from:

#chain=’SSHD’ to


Under the “Add a block rule” section, I changed some iptables commands to ufw commands. You can see the comments ones here:

#firewalladd='iptables -A $chain -p tcp -s $ip --dport 22 -j DROP'
#firewalladd='iptables -A $chain -p tcp -s $ip --dport 22 -j DROP'
firewalladd='ufw insert 1 reject proto tcp from $ip to any port 22'
# Delete a block rule:
firewalldel='ufw delete reject proto tcp from $ip to any port 22'
#firewalldel='iptables -D $chain -p tcp -s $ip --dport 22 -j DROP'

That’s about it! With that, my machine started to grow a big list of IP addresses to block from failed logins.


DNS server not resolving external addresses – bind9 Ubuntu 16.

I ran into issues with Bind 9 on Ubuntu 16 very recently. I use an internal caching DNS server for a few reasons – try to protect myself from malware, log DNS requests on my network to have an idea of where all hosts are going – mainly searching for malware or bad websites, block some domains i.e. ad blocking and some others that I might not want to visit, even by accident, etc. Suddenly at some point, I could no longer resolve any addresses that were not in my zones. My forwarders were no longer working, etc. It turned out to be:

dnssec-validation auto;

This line is default in Ubuntu 16’s Bind 9. Why it worked before, I don’t know. I changed it to

dnssec-validation no;

Then everything magically started working again. Hope this saves someone else’s time. 🙂

Protect your home network using TomatoUSB – how to only allow only HTTP/S out!

While we continue to see the WannaCry and other malware around, I thought I would secure my own network. Since I allow visitors onto their networks, I figured I would configure all new DHCP’d hosts to access the Internet only via HTTP and HTTPs and not allow them to use any DNS servers other than OpenDNS. Here’s how to do it:

The first thing I did was create an access restriction. I did this just to see what chain would be created and I would put subsequent rules into that chain.

access restriction screenshot

The previous screenshot created this chain:

Chain rdev07 (1 references)
target prot opt source destination
DROP all -- anywhere

With this chain, I can add additional rules. The first thing I want to do is allow only DNS access to OpenDNS servers and none other. For this, I would run the following commands:

iptables -A rdev07 -4 -p tcp -s -d --dport 53 -j ACCEPT
iptables -A rdev07 -4 -p udp -s -d --dport 53 -j ACCEPT
iptables -A rdev07 -4 -p tcp -s -d --dport 53 -j ACCEPT
iptables -A rdev07 -4 -p udp -s -d --dport 53 -j ACCEPT
iptables -A rdev07 -4 -p tcp -s -d --dport 53 -j REJECT
iptables -A rdev07 -4 -p udp -s -d --dport 53 -j REJECT

These rules basically allow DNS queries from my network to the 2 OpenDNS servers. The last 2 rules mean that no other DNS servers outside of those 2 servers can be queried. The reason I do this is because there is some malware out there that will change the DNS servers to query on Windows, effectively overriding the DHCP setting. An alternative to this would be to configure Tomato to intercept DNS requests, but I would rather do it this way.

I added the following rules because I had noticed for some reason that some connections coming back from OpenDNS were dropped. I think they’re optional, but I put them in.

iptables -A rdev07 -4 -p tcp -s -d --sport 53 -j ACCEPT
iptables -A rdev07 -4 -p udp -s -d --sport 53 -j ACCEPT
iptables -A rdev07 -4 -p tcp -s -d --sport 53 -j ACCEPT
iptables -A rdev07 -4 -p udp -s -d --sport 53 -j ACCEPT

Next, I go to create my whitelist – this would be my iPhone, iPad, android, etc – any hosts that I trust. I’m going to allow these host to go out to any host with TCP and UDP.


iptables -A rdev07 -4 -p tcp -s -d -j ACCEPT
iptables -A rdev07 -4 -p tcp -s -d -j ACCEPT
iptables -A rdev07 -4 -p tcp -s -d -j ACCEPT
iptables -A rdev07 -4 -p udp -s -d -j ACCEPT
iptables -A rdev07 -4 -p udp -s -d -j ACCEPT
iptables -A rdev07 -4 -p udp -s -d -j ACCEPT
I know that they can still get viruses. I hope they don’t. They can only use OpenDNS for DNS services, but they can access basically anything outside on any port.
Lastly, I configure the rules to allow only HTTP and HTTPs out.
iptables -A rdev07 -4 -p tcp -s -d --dport 80 -j ACCEPT
iptables -A rdev07 -4 -p tcp -s -d --dport 443 -j ACCEPT
iptables -A rdev07 -4 -p all -s -d -j DROP
With this, anyone else on the network can connect to port 80 and 443 of any host on the Internet. Then, any traffic going out to any other port is dropped.
After testing all commands and seeing that they worked for me, I put them all into Administration/Scripts/Firewall.
Inserting custom firewall rules
Have fun and be safe! Please post any comments below.

How to send tweets at random times with a *NIX CLI …

Twitter CLI is a wonderful tool for automatically sending tweets. Very simply, after installation, you just need to run ‘t update “message”‘ and it would tweet your message. I wanted to do some tweeting randomly via cron, but since cron runs regularly at an interval, it’s not very random. Just adding a couple of lines to the script will make it random.

Here’s how to do it.

First, download and install Twitter CLI from here:

Afterwards, make a copy of the t script and call it what you want. I call it randomt:

cp /usr/local/bin/t /usr/local/bin/randomt

Finally, just make a change to the script. Here, I’m setting a variable called time and making it a random number between 1 and 1000. From there, I’m multiplying it by 60 to convert it to minutes.

# This file was generated by RubyGems.
# The application 't' is installed as part of a gem, and
# this file is here to facilitate running it.

require 'rubygems'

version = ">= 0"

time = 1 + rand(1000) * 60

if ARGV.first
 str = ARGV.first
 str = str.dup.force_encoding("BINARY") if str.respond_to? :force_encoding
 if str =~ /\A_(.*)_\z/
 version = $1

gem 't', version
load Gem.bin_path('t', 't', version)

Now, my tweets go out at some random time between 1 and 1000 minutes later. Thanks for reading!



esxtop shows a bunch of stuff … what’s up with this!?

It’s been a while since I’ve had to run esxtop, but when I did recently, I got a bunch of stuff on my screen like this:

o termcap entry for a `xterm-256color’ terminal”(PDH-CSV 4.0) (UTC)(0)”,”\\\Memory\Memory Overcommit (1 Minute Avg)”,”\\\Memory\Memory Overcommit (5 Minute Avg)”,”\\\Memory\Memory Overcommit (15 Minute Avg)”,”\\\Physical Cpu Load\Cpu Load (1 Minute Avg)”,”\\\Physical Cpu Load\Cpu Load (5 Minute Avg)”,”\\\Physical Cpu Load\Cpu Load (15 Minute Avg)”,”\\\Physical Cpu(0)\% Processor Time”,”\\\Physical Cpu(1)\% Processor Time”,”\\\Physical Cpu(2)\% Processor Time”,”\\\Physical Cpu(3)\% Processor Time”,”\\\Physical Cpu(_Total)\% Processor Time”,”\\\Physical Cpu(0)\% Util Time”,”\\\Physical Cpu(1)\% Util Time”,”\\\Physical Cpu(2)\% Util Time”,”\\\Physical Cpu(3)\% Util Time”,”\\\Physical Cpu(_Total)\% Util Time”,”\\\Physical Cpu(0)\% Core Util Time”,”\\\Physical Cpu(1)\% Core Util Time”,”\\\Physical Cpu(2)\% Core Util Time”,”\\\Physical Cpu(3)\% Core Util Time”,”\\\Physical Cpu(_Total)\% Core Util Time”,”\\\Memory\Machine MBytes”,”\\\Memory\Kernel MBytes”,”\\\Memory\NonKernel MBytes”,”\\\Memory\Free MBytes”,”\\\Memory\Kernel Managed MBytes”,”\\\Memory\Kernel MinFree MBytes”,”\\\Memory\Kernel Reserved MBytes”,”\\\Memory\Kernel Unreserved MBytes”,”\\\Memory\Kernel State”,”\\\Memory\PShare Shared MBytes”,”\\\Memory\PShare Common MBytes”,”\\\Memory\PShare Savings MBytes”,”\\\Memory\Swap Used MBytes”,”\\\Memory\Swap Target MBytes”,”\\\Memory\Swap MBytes Read/sec”,”\\\Memory\Swap MBytes Write/sec”,”\\\Memory\Total Compressed MBytes”,”\\\Memory\Total Saved By Compression MBytes”,”\\\Memory\Memctl Current MBytes”,”\\\Memory\Memctl Target MBytes”,”\\\Memory\Memctl Max MBytes”,”\\\Power\Power Usage Now Watts”,”\\\Power\Power Usage Cap Watts”,”\\\Power(0)\P-State MHZ”,”\\\Power(1)\P-State MHZ”,”\\\Power(2)\P-State MHZ”,”\\\Power(3)\P-State MHZ”,”\\\Power(4)\P-State MHZ”,”\\\Power(5)\P-State MHZ”,”\\\Power(6)\P-State MHZ”,”\\\Power(7)\P-State MHZ”,”\\\Power(8)\P-State MHZ”,”\\\Power(9)\P-State MHZ”,”\\\Power(10)\P-State MHZ”,”\\\Power(11)\P-State MHZ”,”\\\Power(12)\P-State MHZ”,”\\\Power(13)\P-State MHZ”,”\\\VSAN\Enabled?”,”\\\Group Cpu(1:idle)\Members”,”\\\Group Cpu(1:idle)\% Used”,”\\\Group Cpu(1:idle)\% Run”,”\\\Group Cpu(1:idle)\% System”,”\\\Group Cpu(1:idle)\% Wait”,”\\\Group Cpu(1:idle)\% Ready”,”\\\Group Cpu(1:idle)\% Idle”,”\\\Group Cpu(1:idle)\% Overlap”,”\\\Group Cpu(1:idle)\% CoStop”,”\\\Group Cpu(1:idle)\% Max Limited”,”\\\Group Cpu(1:idle)\% Swap Wait”,”\\\Vcpu(1:idle:32769:idle1)\% Used”,”\\\Vcpu(1:idle:32769:idle1)\% Run”,”\\\Vcpu(1:idle:32769:idle1)\% System”,”\\\Vcpu(1:idle:32769:idle1)\% Wait”,”\\\Vcpu(1:idle:32769:idle1)\% VmWait”,”\\\Vcpu(1:idle:32769:idle1)\% Ready”,”\\\Vcpu(1:idle:32769:idle1)\% Idle”,”\\\Vcpu(1:idle:32769:idle1)\% Overlap”,”\\\Vcpu(1:idle:32769:idle1)\% CoStop”,”\\\Vcpu(1:idle:32769:idle1)\% Max Limited”,”\\\Vcpu(1:idle:32769:idle1)\% Swap Wait”,”\\\Vcpu(1:idle:32770:idle2)\% Used”,”\\\Vcpu(1:idle:32770:idle2)\% Run”,”\\\Vcpu(1:idle:32770:idle2)\% System”,”\\\Vcpu(1:idle:32770:idle2)\% Wait”,”\\\Vcpu(1:idle:32770:idle2)\% VmWait”,”\\\Vcpu(1:idle:32770:idle2)\% Ready”,”\\\Vcpu(1:idle:32770:idle2)\% Idle”,”\\\Vcpu(1:idle:32770:idle2)\% Overlap”,”\\\Vcpu(1:idle:32770:idle2)\% CoStop”,”\\\Vcpu(1:idle:32770:idle2)\% Max Limited”,”\\\Vcpu(1:idle:32770:idle2)\% Swap Wait”,”\\\Vcpu(1:idle:32771:idle3)\% Used”,”\\\Vcpu(1:idle:32771:idle3)\% Run”,”\\\Vcpu(1:idle:32771:idle3)\% System”,”\\\Vcpu(1:idle:32771:idle3)\% Wait”,”\\\Vcpu(1:idle:32771:idle3)\% VmWait”,”\\\Vcpu(1:idle:32771:idle3)\% Ready”,”\\\Vcpu(1:idle:32771:idle3)\% Idle”,”\\\Vcpu(1:idle:32771:idle3)\% Overlap”,”\\\Vcpu(1:idle:32771:idle3)\% CoStop”,”\\\Vcpu(1:idle:32771:idle3)\% Max Limited”,”\\\Vcpu(1:idle:32771:idle3)\% Swap Wait”,”\\\Vcpu(1:idle:32778:idle0)\% Used”,”\\\Vcpu(1:idle:32778:idle0)\% Run”,”\\\Vcpu(1:idle:32778:idle0)\% System”,”\\\Vcpu(1:idle:32778:idle0)\% Wait”,”\\\Vcpu(1:idle:32778:idle0)\% VmWait”,”\\\Vcpu(1:idle:32778:idle0)\% Ready”,”\\\Vcpu(1:idle:32778:idle0)\% Idle”,”\\\Vcpu(1:idle:32778:idle0)\% Overlap”,”\\\Vcpu(1:idle:32778:idle0)\% CoStop”,”\\\Vcpu(1:idle:32778:idle0)\% Max Limited”,”\\\Vcpu(1:idle:32778:idle0)\% Swap Wait”,”\\\Group Cpu(2:system)\Members”,”\\\Group Cpu(2:system)\% Used”,”\\\Group Cpu(2:system)\% Run”,”\\\Group Cpu(2:system)\% System”,”\\\Group Cpu(2:system)\% Wait”,”\\\Group Cpu(2:system)\% Ready”,”\\\Group Cpu(2:system)\% Idle”,”\\\Group Cpu(2:system)\% Overlap”,”\\\Group Cpu(2:system)\% CoStop”,”\\\Group Cpu(2:system)\% Max Limited”,”\\\Group Cpu(2:system)\% Swap Wait”,”\\\Vcpu(2:system:32772:SVGAConsole)\% Used”,”\\\Vcpu(2:system:32772:SVGAConsole)\% Run”,”\\\Vcpu(2:system:32772:SVGAConsole)\% System”,”\\\Vcpu(2:system:32772:SVGAConsole)\% Wait”,”\\\Vcpu(2:system:32772:SVGAConsole)\% VmWait”,”\\\Vcpu(2:system:32772:SVGAConsole)\% Ready”,”\\\Vcpu(2:system:32772:SVGAConsole)\% Idle”,”\\\Vcpu(2:system:32772:SVGAConsole)\% Overlap”,”\\\Vcpu(2:system:32772:SVGAConsole)\% CoStop”,”\\\Vcpu(2:system:32772:SVGAConsole)\% Max Limited”,”\\\Vcpu(2:system:32772:SVGAConsole)\% Swap Wait”,”\\\Vcpu(2:system:32773:debugtermlivedump)\% Used”,”\\\Vcpu(2:system:32773:debugtermlivedump)\% Run”,”\\\Vcpu(2:system:32773:debugtermlivedump)\% System”,”\\\Vcpu(2:system:32773:debugtermlivedump)\% Wait”,”\\\Vcpu(2:system:32773:debugtermlivedump)\% VmWait”,”\\\Vcpu(2:system:32773:debugtermlivedump)\% Ready”,”\\\Vcpu(2:system:32773:debugtermlivedump)\% Idle”,”\\\Vcpu(2:system:32773:debugtermlivedump)\% Overlap”,”\\\Vcpu(2:system:32773:debugtermlivedump)\% CoStop”,”\\\Vcpu(2:system:32773:debugtermlivedump)\% Max Limited”,”\\\Vcpu(2:system:32773:debugtermlivedump)\% Swap Wait”,”\\\Vcpu(2:system:32774:logSysAlert)\% Used”,”\\\Vcpu(2:system:32774:logSysAlert)\% Run”,”\\\Vcpu(2:system:32774:logSysAlert)\% System”,”\\\Vcpu(2:system:32774:logSysAlert)\% Wait”,”\\\Vcpu(2:system:32774:logSysAlert)\% VmWait”,”\\\Vcpu(2:system:32774:logSysAlert)\% Ready”,”\\\Vcpu(2:system:32774:logSysAlert)\% Idle”,”\\\Vcpu(2:system:32774:logSysAlert)\% Overlap”,”\\\Vcpu(2:system:32774:logSysAlert)\% CoStop”,”\\\Vcpu(2:system:32774:logSysAlert)\% Max Limited”,”\\\Vcpu(2:system:32774:logSysAlert)\% Swap Wait”,”\\\Vcpu(2:system:32775:serialLogger)\% Used”,”\\\Vcpu(2:system:32775:serialLogger)\% Run”,”\\\Vcpu(2:system:32775:serialLogger)\% System”,”\\\Vcpu(2:system:32775:serialLogger)\% Wait”,”\\\Vcpu(2:system:32775:serialLogger)\% VmWait”,”\\\Vcpu(2:system:32775:serialLogger)\% Ready”,”\\\Vcpu(2:system:32775:serialLogger)\% Idle”,”\\\Vcpu(2:system:32775:serialLogger)\% Overlap”,”\\\Vcpu(2:system:32775:serialLogger)\% CoStop”,”\\\Vcpu(2:system:32775:serialLogger)\% Max Limited”,”\\\Vcpu(2:system:32775:serialLogger)\% Swap Wait”,”\\\Vcpu(2:system:32776:tlbflushcount)\% Used”,”\\\Vcpu(2:system:32776:tlbflushcount)\% Run”,”\\\Vcpu(2:system:32776:tlbflushcount)\% System”,”\\\Vcpu(2:system:32776:tlbflushcount)\% Wait”,”\\\Vcpu(2:system:32776:tlbflushcount)\% VmWait”,”\\\Vcpu(2:system:32776:tlbflushcount)\% Ready

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SSH without a password using keys troubleshooting – use RSA instead?

I used a procedure from this:

Basically, you just run ssh-keygen to generate a public key and put it on the server’s ~/.ssh/authorized_keys file and that’s about it. The issue I can into was that the server did not accept DSA keys, but accepted RSA keys.

If you suspect that you’re running into the same problem, you can add the “-v” argument to your ssh command and confirm. You should see something like this:
debug1: Skipping ssh-dss key /Users/altonyu/.ssh/id_dsa – not in PubkeyAcceptedKeyTypes

If that’s the case, try using rsa keys. You can generate the RSA key by running:

ssh-keygen -t rsa

Copy the key over to the server’s authorized_keys file and you should get in immediately!