DNS based revoke lists

May 24, 2008

I just thought about the scaling problem of the SSL revoke lists, I wrote in my last blog post.  The first two solutions that came into mind where peer-to-peer or DNS based ones. Peer-to-peer would be not that good for enterprise users so I took a short look at DNS based revoke list. I just entered it into google and got RFC 2538 back as answer. Thats a full solution for storing certificates in the DNS (and yes also a revoke list). Maybe we could use the revoke list part of this RFC for the SSL revoke lists. This solution would scale without problems and with DNSSEC it would get even more secure.

So why is that not implemented? Just one browser vendor and one CA need to go forward and the rest will follow. They could do that instead of the “green” https stuff which is only there to generate more money. What are your thoughts about this?

The fallout of the Debian OpenSSL security problem

Today I don’t want to write about how the Debian security problem occurred, if it was the fault of the Debian maintainer or the OpenSSL guys. We’re all human so errors can occur, but this shows a much bigger problem we have. Our SSL infrastructure!!

I’m quit sure you read about the weak SSL whitehouse.gov had and that the white house does not handle their SSL stuff by them self, instead the use Akamai for this. If you don’t know Akamai, it is a major content distribution network. They have tens of thousands servers distributed all over the world and the content is served by the closest server to provide higher download speeds for the customs and make a DDOS attack much harder if not impossible. Their customer list includes Microsoft, the New York Times and so on.

So basically the SSL keys of the Akamai servers where weak, and it was possible to get their public keys (it is sent as part of the SSL handshake), and calculate the private ones out of it (there are only 32k possible keys). I know that at least one did it and sent the keys to the CCC, which verify the authenticity of the keys. Sure Akamai replaced their keys immediately. BUT. There is no way to revoke the SSL keys!!

What most people don’t seem to understand so far is that these keys are signed by a CA which is in any browser. This means that a man in the middle attack can easily performed with this. As ATI is also a customer of Akamai, someone could send you a Trojan horse instead of the newest ATI you wanted. SSL has in theory two defenses against this:

  • Keys expire, the Akamai key in October 2008
  • Originally SSL had the idea that CAs publish a list of compromised keys (revoke list) and as part of the SSL handshake the browser should check if a key is on the list. The problem with it was that this does not scale and is a privacy problem too. Browsers don’t implement this or have not activated it by default.

So we’re out in the open for this key until this fall, but that won’t be the end, as e.g. godaddy at least allows to the sign keys for a longer period of time. e.g. 3 years. And the same problem occurs if a private key is leak by other means. The whole foundation of our web security infraction is build on sand. We need something new!!

PS: I want to stress that Akamai did nothing wrong here. They did everything right and still have a problem!

Improving the security of an installed WordPress

May 18, 2008

This weekend was a busy one, due the openssl security problem, I needed to regenerate ssh keys and openvpn certs. After this was I done I thought it is time to improve also the security of my blog.

I looked a little bit around and found the wp-security-scan wordpress plugin, which does a basic scanning of the security of the installation. It found some stuff I had not changed from the default install. For example, I tried to use the plugin to change the tables prefix, but that didn’t work for me, it complained always about missing alter privileges of the db user which was not correct. I then clicked on the link which explained how to do it by hand, but that broke my system a little bit. But I found following blog entry which show how to do it correctly, even how to get the cryptographp plugin working again afterwards.

I know not every blogger has the technical knowledge to secure their blog, but than they should look maybe for a hosted version. For all others with their self hosted blog: Take really a look at the plugin and correct the stuff it reports.

iptables dynamic port script for NFS

May 10, 2008

Some days ago I talked with a friend (here a link to his homepage) about firewalls and file servers and he told me he has a iptables script which adapts to the NFS ports automatically. I asked him for this script and here is it. Thx Hannes for the script.


# rpcinfo -p prints a list of all registered RPC programs
# sed -e '1D' removes the headline
# tr -s ' ' '\t' replaces repeated spaces with a single tab
# cut -f 4,5 we only need the protocol- and port-columns
# sort | uniq removes the duplicate lines
# now we have lines with the needed protocol and port but for splits
# this lines to single words so we have to store the protocol
for l in `rpcinfo -p | sed -e '1D' | tr -s ' ' '\t' | cut -f 4,5 | sort | uniq`
do
  case $l in
    tcp)
      SYN=--syn
      PROTOCOL=$l
        ;;
    udp)
      SYN=
      PROTOCOL=$l
        ;;
    *)
      iptables -A INPUT -p $PROTOCOL --dport $l $SYN -j ACCEPT
    ;;
  esac
done

Online VM builder for VMware Player

Every used VMware Player to “play” precreated VMs? I did, but I thought when I need to create VMs by my own I need VMware Workstation or Virtual PC if was running Windows and not Linux. Ok and there is now VirtualBox, but I never used it before, but as it comes now with Ubuntu 8.04 its changes are raising (no need to compile anything like kernel modules for every security update of the kernel). Anyway I found some thing that allows you to use Vmware Player with your own VMs. Following Websites allow you to create images for VMware Player:

EasyVMX!
VM Builder
vmx-builder.cmd

I think the first is the best one. Maybe this info helps also others, as most of the time VMware Player is enough and someone does not need the Workstation version, and Virtual PC 2007 is bad product. Ever tried to run a current Linux kernel on it. It crashes the kernel. I learned that the hard way with Ubuntu 8.04 server within a Virtual PC 2007. Which was not easy to install in the first place, but booting the current kernel after the installation was the end point of the journey, no problem with VMware Player however.

Kubuntu 8.04 hardy addition packages install script

This script is for my friends, who most know the previous versions already. It installs additional packages for kubuntu 8.04 hardy. I use it for the initial setup of a desktop system. First install Kubuntu from CD and than use this script to get the system which, has all codecs and commonly used programs (be it free or non free software) installed. So this blog entry is for my own reference and for my friends. Basically after running this script you’ll have a system which is ready for usage by a standard user.

Insecurity of Virtual Appliances and some thoughts on 7-zip compression

May 3, 2008

This week I looked for a Ubuntu server 8.04 LTS virtual appliance for Vmware – I found one here. But before I could start testing it I needed to extract the .7z file on my VMware server. The first thing I though was, why the hack 7-zip? Why not use bzip2, which is standard on Linux (beside the faster, but less compressing gzip)?

But I was shown wrong by the first entries at my google search – 7-zip has most of the time the better compression and is not much slower than bzip2. And there is even an open source command line tool on Linux, it is called p7zip. The only thing which prevents me from using it, is that it is not supported by tar so far, as soon that happens I will start using it.

But now to something security related. Almost every virtual appliance I download has openssh as sshd daemon installed. Am I the only guy who things this is a bad idea? The host keys are the same for all virtual appliances. So anyone who knows which virtual appliances I used to setup my server, can use this knowledge to perform a man in the middle attack and get my login name and password. This bad habit seems to occur by almost all virtual appliances I got my hands on. My solutions so far is following on Ubuntu and Debian Systems:


apt-get --purge remove openssh-server && apt-get install ssh

This way I’ve a clean config and new keys. (ssh is a meta package for openssh-client and openssh-server). So there is a easy work around but how many administrators will think about that? I think virtual appliances are made to ease the life of the administrators or to allow even non expert to provide a service based on the appliance. With this goal comes also the responsibility to make the system save by default.

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