October 24, 2014
It got fixed with Ubuntu 14.04 but 12.04 is still supported and many people are still using 12.04 and even with the OpenSSL package update (2014-10-02) TLS 1.2 is not enabled by default. Take a look at this bug report and the statement from Marc Deslauriers (Ubuntu Security Engineer):
That USN doesn’t re-enable TLSv1.2 by default for clients in Ubuntu 12.04. It simply fixes an issue if someone _forced_ TLSv1.2 to be enabled.
You’re asking why we got into that problem in the first place … Marc tells us also this:
Ubuntu 12.04 contains openssl 1.0.1, which supports TLS v1.2. Unfortunately, because of the large number of sites which incorrectly handled TLS v1.2 negotiation, we had to disable TLS v1.2 on the client.
So someone thought again he is smarter than the OpenSSL guys … but this was not the first time …. lets remember this “optimization” of OpenSSL by the Debian guys .. could they please clean up their mess and enable TLS 1.2 by default as in 14.04?
October 13, 2014
Just as information for you guys using Mikrotik’s RouterOS but who don’t monitor the wiki for changes or are regular readers of the forum. Mikrotik changed its license concerning the updates. Before this summer following paragraph was on their license wiki page:
You can take a look at the full old version here. Anyway this whole paragraph has been removed. Also with RouterOS 6.20 the following got removed when typing
/system license print on the router:
So what does that mean now? jarda from the forums put it nicely:
October 12, 2014
At the Black Hat conference this year researchers from Berlin-based Security Research Labs (SRLabs) showed an attack method they called “BadUSB“, which allowed them, with manipulated USB device firmwares (e.g. from a USB Stick), to simulate an keyboard. With this keyboard they executed commands on the victims computer without he/she knowing it. The victim just inserted a USB stick to copy some data …. but the new keyboard executes some commands in the background.
To protect yourself against such an attack the computer needs to configured in a way that it does not bind any newly added device as new keyboard without asking the user. For Linux there is a kernel feature starting with 2.6.13-rc3 ( = since 2005) which allows to bind and unbind drivers from devices manually from user space. More information can be found on this topic here and here. And this blog post from Christian Vogel shows how to use it against BadUSB. What is currently missing is a simple GUI program which allows you to allow/deny devices with on click.
On the Windows site there is already such a program. This freeware program is made by the German security vendor (e.g. anti virus software) G DATA and is called “G DATA USB KEYBOARD GUARD” and can be downloaded from here. After installing you’ll be prompted following screen if a new keyboard is inserted.
It would be nice if the various desktop environments on Linux add a similar feature … the kernel support is there already.
October 6, 2014
I found a small program called Lynis, which does a system check of your Linux and Unix System. From the homepage:
Lynis is an open source security auditing tool. Primary goal is to help users with auditing and hardening of Unix and Linux based systems. The software is very flexible and runs on almost every Unix based system (including Mac). Even the installation of the software itself is optional!
To test a system is really easy, just download the tar.gz from here and extract the tar as root (otherwise it will complain) and change into its directory and call
for the interactive mode (waits after each section) or
for the quick mode which only logs the results to the log file. In both cases the log is written to
For the following screenshots a I did setup a test system with some changes to show you some errors and warnings :-):
and at the end you get a summary with entries like this:
And you’ll get also a “Hardening index” which allows you to compare various systems against each other.
I you want to check multiple systems it it also possible to create an rpm file with the
lynis.spec file from the Lynis homepage. You should run this software every time you setup a new system to make sure that you didn’t leave the big whole open.
September 17, 2014
For some time now I wondered why I had such a high CPU load while watching e.g. YouTube videos, even if I’ve a Nvidia GeForce GTX 760 in my PC. Ok thats not the latest card, but normal HD video should be accelerated with it also. 20% CPU load on my modern CPU is too much for a simple YouTube video:
The solution is quite easy – the flash player has disabled the hardware acceleration by default. Following steps need to be done to enable it – as I only have an Nvidia card I was only able to test it for it, but looking around I found some tips for the other cards too.
- Check if you’ve
libvdpau1installed. On Ubuntu its done like this:
# dpkg -l | grep vdpau
ii libvdpau1:amd64 0.7-1 amd64 Video Decode and Presentation API for Unix (libraries)
- You need a fitting graphics card driver:
- Nvidia: Nouveau and Closed Source driver should work
- AMD Radeon: You need the Mesa projects drivers (r300g, r600g or radeonsi)
- Intel: You need also following library/packaged installed:
libvdpau-va-gl1(as Intel supports only the libva interface for video acceleration)
- You need (most likely) to create following file
/etc/adobe/mms.cfgwith following content. It is possible that the directory and file exists in this case add the lines:
- Now you need to make sure that the player is not running anymore:
# ps aux | grep plugin-containe
robert 8246 0.1 0.9 798312 153260 ? Sl Sep16 0:57 /usr/lib/firefox/plugin-container /usr/lib/flashplugin-installer/libflashplayer.so -greomni /usr/lib/firefox/omni.ja -appomni /usr/lib/firefox/browser/omni.ja -appdir /usr/lib/firefox/browser 7066 true plugin
# kill 8246
- Now open the YouTube page again you tried before and top should show following – under 10% CPU Load, thats better.
August 24, 2014
Some time ago I wrote a blog post on Burp as a MitM Proxy (Man-in-the-Middle) – now there is for some purposes an even easier way. The US-CERT has released the first version of a virtual appliance with the name Tapioca (Transparent Proxy Capture Appliance). With it, it is easy to check if programs don’t do certificates validation correctly. I really recommend to try it out! Some areas that are often good for a bad implementations are: mobile apps, hardware and embedded devices and generally stuff that needs a high domain specify know how and that often goes with less software engineering know how.
August 10, 2014
For readers with their own mail server (or if you want to check what your provider is doing) – verify that your mail server accepts encrypted communication and that PFS is enabled. Just click on this link and enter the domain name to test. Some big players goof there …. It should at least look like in the screen shot. DANE would be cool, but that’s not that easy at this point as you need a working DNSsec DNS server, which not all registrars provide. Sure you can host your own authoritative DNS servers but that is work …
ps: send also a mail to [email protected] to check if sending mails is also encrypted. It should look like this:
Today I ran into my first IPv6 problem … all was easy so far for some years .. just configured it and it worked … but this weekend I deployed a second Internet connection for my home. With IPv4 and masquerading the internal IP addresses to the one provider-given IP addresses I was able on the router to configure which traffic goes out over which provider. If one provider fails the route is withdrawn and all goes over the other link. But now comes IPv6 and it is not that easy anymore, as my router does not support IPv6 NAT. The problem is described in detail in this nice blog post by Ivan Pepelnjak.
My router is able to do VRF (Virtual Routing and Forwarding) also for IPv6 (at least the documentation says so .. didn’t try it so far). So the “best” option for me seems to advertise both subnets the providers gave me to the clients and route source based to the providers. Without VRF I would be depended that the providers don’t do a RPF (Reverse Path Forwarding) check, which is also not a good idea. But this leads to the problem that the end device decides which uplink it uses, which is most likely not the one I would choose ….
An other idea was to use one of my servers in a data center to tunnel the traffic through. Basically running two IP tunnels from my router to the server (one via each provider) and using IP addresses that are routed from the Internet to the server. But this is also not a good solution.
Anyway I don’t have good solution so far, maybe one of my readers does.
August 1, 2014
In the last days I encountered a problem with the DNS resolution by our Linux systems – must be there for a long time but it took a deep look into a different performance problem to get this one figured out. I did a simple wget to a HTTP site in the same data center and it took sometimes 5 seconds to get DNS name resolved to an IP address. As a network guy I launched tcpdump at once and did see following packets:
10:59:19.264987 IP LinuxClient.51463 > WindowsDnsServer.domain: 57223+ A? xxxx.penz.name. (35)
10:59:19.265056 IP LinuxClient.51463 > WindowsDnsServer.domain: 26702+ AAAA? xxxx.penz.name. (35)
10:59:19.265700 IP WindowsDnsServer.domain > LinuxClient.51463: 26702* 0/1/0 (103)
10:59:24.269981 IP LinuxClient.51463 > WindowsDnsServer.domain: 57223+ A? xxxx.penz.name. (35)
10:59:24.270303 IP WindowsDnsServer.domain > LinuxClient.51463: 57223* 1/0/0 A 10.10.xxx.xxx (51)
10:59:24.270370 IP LinuxClient.51463 > WindowsDnsServer.domain: 26702+ AAAA? xxxx.penz.name. (35)
10:59:24.270557 IP WindowsDnsServer.domain > LinuxClient.51463: 26702* 0/1/0 (103)
As you see the first A query gets not answered but the AAAA does. I changed to an other DNS server (first Windows 2008 R2 and the second Windows 2012 R2) but with the same results. I did tests with RHEL6/Centos6 and Ubuntu 14.04 .. no difference. As a next step I talked with the Windows guys to look at the Windows 2012 R2 DNS server. They did a packet capture and saw that the Windows server did not send that packet, but a DNS Debug log showed that the DNS server it self did answer it. I than called wget with the “–inet4-only” option, which made sure that only a A query was sent and I was not able to reproduce the problem. So it must be something with the second packet.
Getting a tip from a fellow network admin who said I should look at the source port of the packets I did so. The UDP source ports of the A and AAAA were the same and it looked like that the Linux system gets an answer if the A query is answered before the AAAA arrives on the Windows Server. The next step was to look for a way to change that behavior on the Linux side, which looked to me easier than to change something on the Windows site.
Following resolv.conf option looked promising:
single-request-reopen (since glibc 2.9)
The resolver uses the same socket for the A and AAAA requests. Some hardware mistakenly sends back only one reply. When that happens the client system will sit and wait for the second reply. Turning this option on changes this behavior so
that if two requests from the same port are not handled correctly it will close the socket and open a new one before sending the second request.
And yes – that was the solution. On every system I added
/etc/resolv.conf the problem went away. For systems which generate the
resolv.conf automatically (like Ubuntu 14.04), which you can check by
lrwxrwxrwx 1 root root 29 Mai 26 12:35 /etc/resolv.conf -> ../run/resolvconf/resolv.conf
you should add the line to
/etc/resolvconf/resolv.conf.d/base instead and call
sudo resolvconf -u afterwards.
All together this problem took me many hours to find and I didn’t find anything on the net .. so I thought a post may help other poor admins.
July 18, 2014
Many people got new debit cards (called “Bankomatkarte in Austria) from the various bankings institutes in the last months and years. Many cards are PayPass enabled for wireless money transactions. PayPass is based on NFC, which is also integrated in some of the modern smart phones. The default setting is that five 25 Euro transactions can be done without entering a PIN. So a possible damage can be up to 125 Euro. You’ll verify if your debit card supports that standard by checking it has PayPass printed on it.
Picture: Maestro PayPass
But I’ve seen some cards with only this symbol (at least on the front side):
Anyway in therapy the card needs to be within 10cm of the reader and therefore an attack is not that easy. But already at Defcon 20 in 2012 Eddie Lee presented the possible of a NFCProxy which allows to misuse a card. The attack setup looks like this:
Picture: Eddie Lee @ Defcon 20
So this allows following attack vector. You’re standing in a crow or in a line and have your debit card in your back pocket. One of the attacker stands behind you …. and the other can be e.g. hundred meters away (only limited by the delay and reach of the network connection). They will be able to get your money with much less risk than with pocket picketing. And to make it even better – you can download the App for Android as an .apk file, ready to install and use, from Sourceforge.
So now you know of the problem, what can you to mitigate that problem?
- If you don’t need that feature at all, try to talk to your bank to disable that function. Some will do it for free, others will charge you. Some banks allow to you to choose if you want one with or without at renewal of your card.
- You basically like the feature, but you would like to have more control over it – thats also possible:
- Search for RFID/NFC blocking sleeves for credit card or payment cards
- You can get also wallets with RFID/NFC blocking feature … but currently they look not that great .. at least the ones I found