Internet Storm Center on the Spamhaus DOS

The Internet Storm Center (ISC) has a blog post up discussing the DOS attack against Spamhaus. They do confirm they saw traffic approaching 300Gbps against Spamhaus. They also point out that most people probably never knew.

The attack was significant, but not globally so despite the media reports to the contrary. When news of the attack reached the Internet Storm Center, we did have a brief moment of panic and contemplated resorting to cannibalism. However, we quickly decided against this option (due to a combination of calmer heads prevailing and a lack of consensus on whether people could be turned into bacon).

ISC has a lot of technical details about how to secure your DNS servers, and I strongly encourage everyone to go look and make sure their DNS servers are secure. I checked ours a few days ago. I really didn’t think they would be open; Steve gets DNS and keeps up with security so it was unlikely we had open resolvers. I looked up our resolvers anyway because a second pair of eyes on things is never a bad thing.

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The view from a blacklist operator

We run top-level DNS servers for several blacklists including the CBL, the blacklist of infected machines that the SpamHaus XBL is based on. We don’t run the CBL blacklist itself (so we aren’t the right people to contact about a CBL listing) we just run some of the DNS servers – but that means that we do get to see how many different ways people mess up their spam filter configurations.
This is what a valid CBL query looks like:

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More on the attack against Spamhaus and how you can help

While much of the attack against Spamhaus has been mitigated and their services and websites are currently up, the attack is still ongoing.  This is the biggest denial of service attack in history, with as much as 300 gigabits per second hitting Spamhaus servers and their upstream links.
This traffic is so massive, that it’s actually affecting the Internet and web surfers in some parts of the world are seeing network slowdown because of this.
While I know that some of you may be cheering at the idea that Spamhaus is “paying” for their actions, this does not put you on the side of the good. Spamhaus’ actions are legal. The actions of the attackers are clearly illegal. Not only is the attack itself illegal, but many of the sites hosted by the purported source of the attacks provide criminal services.
By cheering for and supporting the attackers, you are supporting criminals.
Anyone who thinks that an appropriate response to a Spamhaus listing is an attack on the very structure of the Internet is one of the bad guys.
You can help, though. This attack is due to open DNS resolvers which are reflecting and amplifying traffic from the attackers. Talk to your IT group. Make sure your resolvers aren’t open and if they are, get them closed. The Open Resolver Project published its list of open resolvers in an effort to shut them down.
Here are some resources for the technical folks.
Open Resolver Project
Closing your resolver by Team Cymru
BCP 38 from the IETF
Ratelimiting DNS
News Articles (some linked above, some coming out after I posted this)
NY Times
BBC News
Cloudflare update
Spamhaus dDOS grows to Internet Threatening Size
Cyber-attack on Spamhaus slows down the internet
Cyberattack on anti-spam group Spamhaus has ripple effects
Biggest DDoS Attack Ever Hits Internet
Spamhaus accuses Cyberbunker of massive cyberattack

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Setting up DNS for sending email

Email – and email filtering – makes a lot of use of DNS, and it’s fairly easy to miss something. Here are a few checklists to help:

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