Threat Level: green Handler on Duty: Renato Marinho

SANS ISC: Debian and Ubuntu users: fix your keys/certificates NOW - SANS Internet Storm Center SANS ISC InfoSec Forums


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Debian and Ubuntu users: fix your keys/certificates NOW

Couple of days ago Swa posted a diary about a critical Debian/Ubuntu PRNG security vulnerability.

Today Matt wrote in to let us know that H D Moore posted a web page containing all SSH 1024, 2048 and 4096-bit RSA keys he brute forced.

It is obvious that this is highly critical – if you are running a Debian or Ubuntu system, and you are using keys for SSH authentication (ironically, that's something we've been recommending for a long time), and those keys were generated between September 2006 and May 13th 2008 then you are vulnerable. In other words, those secure systems can be very easily brute forced. What's even worse, H D Moore said that he will soon release  a brute force tool that will allow an attacker easy access to any SSH account that uses public key authentication.

But this is not all – keep in mind that ANY cryptographic material created on vulnerable systems can be compromised. If you generated SSL keys on such Debian or Ubuntu systems, you will have to recreate the certificates and get them signed again. An attacker can even decrypt old SSH sessions now.

The Debian project guys released a tool that can detect weak keys (it is not 100% correct though as the blacklist in the tool can be incomplete). You can download the tool from http://security.debian.org/project/extra/dowkd/dowkd.pl.gz.

 
The bottom line is: this is very, very, very serious and scary. Please check your systems and make sure that you are both patched, and that you regenerated any potentially weak cryptographic material.

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Bojan

Bojan

359 Posts
ISC Handler
Are we certain that only Debian and Ubuntu are affected? SSH key generation happens in many different systems, and who knows what they may be using to generate those keys or how (in)secure they may be...
Lee

21 Posts Posts
For this particular bug we know that it was introduced in Debian's PRNG. Since other distributions don't use Debian's PRNG they are not affected, at least not by this vulnerability.
Bojan

359 Posts Posts
ISC Handler
From what I can find, puTTy and its various utilities use the vulnerable Debian PRNG to generate SSH keys. Is this related?

See: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=400804
Lee

21 Posts Posts
I didn't know the putty tools were included in Debian (what's the point really?), but I would assume they are safe since they do not depend on the libssl package which contains the libraries of OpenSSL, where the original bug was. See: http://packages.debian.org/etch/putty-tools
Alexandre

1 Posts Posts

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