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What can I do today to avoid the new SSL vulnerability?

I have been listening to the Security Now podcast, episode 223: "The Trouble With SSL". MP3 for episode 223 (42 MB). Transcript.
Update: nine episode later, episode 232 (2010-01-22), 23 min 00 secs - 28 min 45 secs, there is a description of IETF's ratified fix for the vulnerability. MP3 for episode 232 (48 MB). Transcript. There is also an article at eWeek: "IETF Completes Fix for SSL Security Vulnerability". IETF draft, RFC 5746.

As I understood it it is a very serious man-in-the-middle vulnerability and either the operating system needs to be updated or the client could refuse renegotiation (I am not sure if the client is the web browser or the operating system).

What software has been updated? I am normally on Windows XP, but I would be willing to install some version of Linux to avoid this problem. Is it sufficient to install an updated web browser?

I want to purchase something online and want to be sure not being hit by this problem.

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What makes you think that in the thousands of SSL-secured transactions that happen every minute, yours could be at risk? Same as asking "how can I make sure a bus doesn't drive on me"? It might happen but it's so rare, is it worth making special arrangements for this? – Snark Nov 26 '09 at 23:12
up vote 4 down vote accepted

Short answer: You can 1) wait, 2) avoid connections to important servers on public access points.

First of all, don't get overly scared. Remain calm, and listen to the followup episodes which will surely deal with fixing or circumventing the problem.

As far as I understand, what the described attack makes possible is creating a single TLS (aka SSL) secured request that's can be made look like it's authenticated. The man-in-the-middle will never get to read anything from the connection, he can only insert one malicious request to the beginning of a secure stream. The attacker cannot even read the reply, so he has to rely on doing an requesting an malicious action.

But you are right, this situation does require updating all secure web servers. It cannot be prevented on the client side, so there's no use updating your system. What clients could do is ask if the server happens to know how to prevent this, and simply drop the connection if the server doesn't know anything about it. But... "you know, if we told our browsers not to allow TLS without renegotiation protection, we couldn't talk to anybody today." So that protection ends up being the same as simply avoiding TLS.

But before there is a fix... well the fact remains that any TLS connection opened on a public access point could get silently preceded by a one-way malicious request. Of course you woudn't want that reqeust to say "transfer X money to this Y account". :) But then again, bank transactions like that require multiple page loads and credential communication, so I don't see any risk there.

And there are worse and more likely threats out there too. This one is just particularly interesting, since there seems to be no way of currently avoiding it. Security people get interested about things like that. The reality seems to be that people can be spoofed a lot more seriously and more easily (simples one is man-in-the-middle turning all HTTPS to unsecure HTTP, and most people won't notice it), so I don't see why someone would bother with this attack. But yeah, to be on the safe side, I would advise on not opening connections to important services on public access points.

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Thanks for providing actual/specific information about this particular vulnerability. And for your analysis and conclusion. – Peter Mortensen Dec 11 '09 at 12:05
Well, most of the information comes from the same (great) episode, hopefully I got it right. :) I did read a few articles about it for checkup too, though - it's really is an interesting vulnerability. – Ilari Kajaste Dec 12 '09 at 22:02

Here is a great answer by Bruce Schneier, from which I quote:

Should you not use SSL until it's fixed, and only pay for internet purchases over the phone? Should you download some kind of protection? Should you take some other remedial action? What?

If you read the IT press regularly, you'll see this sort of question again and again. The answer for this particular vulnerability, as for pretty much any other vulnerability you read about, is the same: do nothing. That's right, nothing. Don't panic. Don't change your behavior. Ignore the problem, and let the vendors figure it out.

The reasons for that are explained in the blog post.

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A particularly good quote from that post is: "the odds of a particular vulnerability affecting you are small. There are a lot of fish in the Internet, and you're just one of billions." – Ilari Kajaste Dec 11 '09 at 11:12

Don't listen to people who try to scare you! This certainly is not worth changing operating system over.

Just use your internet like normal with your usual DNS provider and don't worry so much. Man in the middle attacks require... a man in the middle and on a standard network, this just doesn't really happen.

If you use Wireless, make sure you are using WPA2 and rotate your keys often, and if using wired, I wouldn't worry.

Don't use public access points as this is where you will most likely run into someone who uses this sort of attack.

Make sure you use a good DNS provider such as OpenDNS.

At the end of the day, your ISP could have a custom route for some IPs and be forging ALL DNS requests, they can block/log/re route anything... Anything can happen in life... Sometimes, you just have to get on with life and balance the pros with the cons!

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"Don't listen to people who try to scare you!" especially NOT to Steve Gibson!!! :D – Molly7244 Nov 26 '09 at 23:31
Um, I don't think DNS has anything to do with this problem... – Ilari Kajaste Dec 11 '09 at 10:45
While your ISP can mess up with standard connections any way it wants, even the ISP couldn't break a TLS connection. No matter rerouring or forging, TLS is end-to-end, browser-to-server secure. Or, well, it was. :) – Ilari Kajaste Dec 11 '09 at 10:49
And, if you ask me, the glory days of OpenDNS are over as well. Too much spying for my liking. Try a ping -- yes, I know they claim it's to stop Dell computers from redirecting typos to Google, Still, ... – Arjan Jan 11 '10 at 10:57

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