OpenSSL worked on Easily Guessable Key

BIG BUG : OpenSSL worked on Easily Guessable Key

After Debian's epic SSL blunder, a world of hurt for security pros

By Dan Goodin in San Francisco

21st May 2008

http://www.theregister.co.uk/2008/05/21/massive_debian_openssl_hangover/

It's been more than a week since Debian patched a massive security hole in the library the operating system uses to create cryptographic keys for securing email, websites and administrative servers. Now the hard work begins, as legions of admins are saddled with the odious task of regenerating keys too numerous for anyone to estimate.

The flaw in Debian's random number generator means that OpenSSL keys generated over the past 20 months are so predictable that an attacker can correctly guess them in a matter of hours. Not exactly a comforting thought when considering the keys in many cases are the only thing guarding an organization's most precious assets. Obtain the key and you gain instant access to trusted administrative accounts and the ability to spoof or spy on sensitive email and web servers.

Security pros have rightfully reacted swiftly to word of Debian debacle. But if you think last week's patch is like most other security fixes, you're dead wrong. Installing it is probably the easiest part of mopping up the resulting mess. Once it's installed, admins will be forced to search sometimes sprawling systems for every key that's ever interacted with the buggy version of Debian and a host of other OSes and applications that relied on it.

Certificates for defective keys will have to be revoked, new keys will have to be generated and, in the case of SSL certificates, registered with VeriSign or another certificate authority. No one knows how many keys need to be replaced, but it could number in the hundreds of thousands or millions. The keys are used for Secure Sockets Layer (SSL) transactions, which authenticate servers handling trusted websites and email, and to authenticate Secure Shell (SSH), which provides encrypted channels between sensitive computers.

The heft and tedium of tracking down, testing and regenerating so many keys, and the cost of paying certificate authorities to register them, has left some people feeling pessimistic about the prospects the problem will be fixed anytime soon.

"There's the pain-in-the-ass factor and then there's the cost factor," says Jacob Appelbaum, an independent security researcher, as he ticks off the reasons he believes organizations will be slow to tackle the problem. Sure, some will make an earnest effort, but "even those people are going to be overwhelmed and patch a lot of their systems but not all of them," he adds.

Weakened White House

Among the weak SSL certificates at time of publication is this one belonging to Whitehouse.gov. It's of little consequence, since the site doesn't conduct secure transactions, but it does show the ubiquity of the problem. The key is owned by content delivery provider Akamai Technologies and is used by about 20,000 websites. Akamai is in the process of replacing it.

Akamai has escaped relatively unscathed. All its keys involved in sensitive transactions are generated using a highly customized Debian derivative that didn't include the buggy random number generator. The single key used by Whitehouse.gov and the other Akamai customers, which was generated using a separate system running on standard Debian is the only one affected, says Andy Ellis, Akamai's senior director of information security.

"I can't imagine how painful this will be for people who are using large data centers with hundreds of certificates," Ellis said.

The unwieldy cleanup effort is akin to the aftermath of a serious Flash vulnerability found in December to be plaguing tens of thousands of websites. Three months after a patch was released, the sites - many carrying out banks financial and other sensitive transactions - remained vulnerable because they had yet to remove and regenerate an estimated 500,000 buggy flash applets. Both the Debian and Flash vulnerabilities are unusual, because applying the patch represents only the beginning of the healing process.

The Debian bug was introduced in September 2006. It vastly reduces the amount of entropy used when programs like the Apache webserver, Sendmail, Exim and some implementations of Kerberos use OpenSSL to perform basic cryptographic functions. As a result, attackers can crack SSL keys, x.509 certificate keys, SSH keys, and digital signatures in fewer than 33,000 guesses, rather than the seemingly-infinite number of tries that would normally be required.

Tools available from Ubuntu and Metasploit author HD Moore are designed to aid in the process of detecting weak keys, but Appelbaum, the independent researcher, says certain conditions will prevent even diligent searches from finding everything. For example, keys with nonstandard sizes may not be flagged even though they're vulnerable.

"What that means is you have tools that may cover large swaths of the key space, but they won't cover all of the key space," he says.

So if your organization hasn't begun a thorough audit of all the keys in its portfolio, now is the time to get to it. Like an outbreak of lice at the children's grade school, its an unpleasant task eradicating the pests, but it's got to be done.

"This is a bit of a nightmare for anybody who used Debian" or programs that relied on its OpenSSL library, says Vincent Danen, the security team manager for Mandriva, a Linux distribution that was not affected by the bug. "If you're running a Debian shop and you have 100 certificates, depending on who you've got as a certificate authority, you could be looking at big bucks to regenerate your keys and get them re-signed. It could take months or even years for all the keys to get weeded out."