Heartbeat SSL Flaw Puts Linux Distros at Risk

NEWS ANALYSIS: Hours after the flaw's disclosure, many Linux distributions didn't have a patch. Now that a fix is out, OpenSSL users should make sure to update their servers.

Linux server security

The Secure Sockets Layer (SSL) is at the foundation of all Web based communications, and when security flaws are found, immediate fixes are required. On April 7, the open-source OpenSSL project issued an advisory regarding a critical vulnerability that could potentially leave millions of users at risk.

The flaw—identified as CVE-2014-0160 and called "TLS heartbeat read overrun"—has been present in OpenSSL since March 2012, but it was just recently discovered.

However, the flaw has been unofficially dubbed "Heartbleed" by security research firm Codenomicon, which is the name that has caught on in most subsequent media reports.

"A missing bounds check in the handling of the TLS [Transport Layer Security] heartbeat extension can be used to reveal up to 64k of memory to a connected client or server," the OpenSSL advisory warns.

OpenSSL is an open-source SSL library that is widely used in conjunction with Web servers and Linux distributions. The flaw was first reported by Neel Mehta of Google's security team, and the OpenSSL project has issued a fix with the new OpenSSL 1.0.1g update.

Researchers with security firm Codenomicon also claim to have discovered the flaw. In a Web page FAQ list on the Heartbeat flaw, Codenomicon explains that the CVE-2014-0160 bug is in the OpenSSL's implementation of the TLS/DTLS, or Transport Layer Security/Datagram Transport Layer Security, heartbeat extension (RFC6520).

"When it is exploited, it leads to the leak of memory contents from the server to the client and from the client to the server," Codenomicon states.

What that means is that sessions that were encrypted could be decrypted, thanks to a memory leak. Going a step further, given that most Web servers use a single-server key to encrypt SSL, all communications with a vulnerable server could potentially be at risk.

Aside from updating to the new version of OpenSSL, Web server administrators should also consider implementing Perfect Forward Secrecy (PFS). PFS is a technique that creates a new unique session key for each encrypted session that would limit the risk of retrospective decryption. (A recent eSeminars Live event offers insight on PFS).

The other big issue with the Heartbeat flaw is how the bug was actually disclosed. Yes, the OpenSSL project only released its advisory after it had a fix, which is a good idea; however OpenSSL use is much wider than just the OpenSSL project. Each individual Linux distribution has its own packaged version of OpenSSL that needs to be updated, as well.

I contacted Red Hat late in the afternoon on April 7, and at the time, they were aware of the issue but did not yet have a patch available for users. At 11 p.m., I received an email from Red Hat's Fedora project notifying me that new OpenSSL packages were available to fix the flaw. Red Hat Enterprise Linux users got access to the patch early on April 8.

While Red Hat and other Linux vendors did not have patches immediately available when the OpenSSL advisory was released, cloud security vendor CloudFlare did. In a blog post, CloudFlare claims to have fixed the CVE-2014-0160 flaw before it became public.

"As one of the largest deployments of OpenSSL on the Internet today, CloudFlare has a responsibility to be vigilant about fixing these types of bugs before they go public and attackers start exploiting them and putting our customers at risk," CloudFlare blogged.

It is unclear how CloudFlare was able to get access to the flaw information before a big Linux vendor like Red Hat. A proper responsible bug disclosure process should have included all stakeholders so that all affected parties could issue a fix at the same time. With the CVE-2014-0160 flaw, there was a small window of exposure from the time the OpenSSL project issued its advisory and CloudFlare blogged on the issue, until Linux projects had patches available for users. That's just not right and could have put millions of people at unnecessary risk.

In any event, it is incumbent on all OpenSSL users to immediately make sure that they are not at risk today and have updated their servers.

Sean Michael Kerner is a senior editor at eWEEK and InternetNews.com. Follow him on Twitter @TechJournalist.

Editor's Note: This story has been updated to include the "Heartbleed" unofficial name for the "TLS heartbeat read overrun" flaw reported by the OpenSSL Project.

Sean Michael Kerner

Sean Michael Kerner

Sean Michael Kerner is an Internet consultant, strategist, and contributor to several leading IT business web sites.