Apr 08 2014

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This is nasty. There is a remotely exploitable bug in openssl which leads to the leak of memory contents from the server to the client and from the client to the server. In practice this means that an attacker can read 64K chunks of memory on a vulnerable service, thus potentially exposing security critical information.

At 19.00 UTC yesterday, openssl bug CVE-2014-0160 was announced at heartbleed.com. I picked it up following a flurry of emails on the tor relays list this morning. Roger Dingledine posted a blog commentary on the bug to the tor list giving details about the likely impacts on Tor and Tor users.

Dingledine’s blog entry says:

Here are our first thoughts on what Tor components are affected:

  • Clients: Tor Browser shouldn’t be affected, since it uses libnss rather than openssl. But Tor clients could possibly be induced to send sensitive information like “what sites you visited in this session” to your entry guards. If you’re using TBB we’ll have new bundles out shortly; if you’re using your operating system’s Tor package you should get a new OpenSSL package and then be sure to manually restart your Tor.
  • Relays and bridges: Tor relays and bridges could maybe be made to leak their medium-term onion keys (rotated once a week), or their long-term relay identity keys. An attacker who has your relay identity key can publish a new relay descriptor indicating that you’re at a new location (not a particularly useful attack). An attacker who has your relay identity key, has your onion key, and can intercept traffic flows to your IP address can impersonate your relay (but remember that Tor’s multi-hop design means that attacking just one relay in the client’s path is not very useful). In any case, best practice would be to update your OpenSSL package, discard all the files in keys/ in your DataDirectory, and restart your Tor to generate new keys.
  • Hidden services: Tor hidden services might leak their long-term hidden service identity keys to their guard relays. Like the last big OpenSSL bug, this shouldn’t allow an attacker to identify the location of the hidden service, but an attacker who knows the hidden service identity key can impersonate the hidden service. Best practice would be to move to a new hidden-service address at your convenience.
  • Directory authorities: In addition to the keys listed in the “relays and bridges” section above, Tor directory authorities might leak their medium-term authority signing keys. Once you’ve updated your OpenSSL package, you should generate a new signing key. Long-term directory authority identity keys are offline so should not be affected (whew). More tricky is that clients have your relay identity key hard-coded, so please don’t rotate that yet. We’ll see how this unfolds and try to think of a good solution there.
  • Tails is still tracking Debian oldstable, so it should not be affected by this bug.
  • Orbot looks vulnerable; they have some new packages available for testing.
  • The webservers in the https://www.torproject.org/ rotation needed (and got) upgrades too. Maybe we’ll need to throw away our torproject SSL web cert and get a new one too.

But as he also says earlier on, “this bug affects way more programs than just Tor”. The openssl security advisory is remarkably sparse on details, saying only that “A missing bounds check in the handling of the TLS heartbeat extension can be used to reveal up to 64k of memory to a connected client or server.” So it is left to others to explain what this means in practice. The heartbleed announcement does just that. It opens by saying:

The Heartbleed Bug is a serious vulnerability in the popular OpenSSL cryptographic software library. This weakness allows stealing the information protected, under normal conditions, by the SSL/TLS encryption used to secure the Internet. SSL/TLS provides communication security and privacy over the Internet for applications such as web, email, instant messaging (IM) and some virtual private networks (VPNs).

The Heartbleed bug allows anyone on the Internet to read the memory of the systems protected by the vulnerable versions of the OpenSSL software. This compromises the secret keys used to identify the service providers and to encrypt the traffic, the names and passwords of the users and the actual content. This allows attackers to eavesdrop communications, steal data directly from the services and users and to impersonate services and users.

During their investigations, the heartbleed researchers attacked their own SSL protected services from outside and found that they were:

able to steal from ourselves the secret keys used for our X.509 certificates, user names and passwords, instant messages, emails and business critical documents and communication.

According to the heartbleed site, versions 1.0.1 through 1.0.1f (inclusive) of openssl are vulnerable. The earlier 0.9.8 branch is NOT vulnerable, nor is the 1.0.0 branch. Unfortunately, the bug was introduced to openssl in December 2011 and has been available in real world use in the 1.0.1 branch since 14 March 2102 – or just over 2 years ago. This means that a LOT of services will be affected and will need to be patched, and quickly.

Openssl, or its libraries, are used in a vast range of security critical services across the internet. As the heartbleed site notes:

OpenSSL is the most popular open source cryptographic library and TLS (transport layer security) implementation used to encrypt traffic on the Internet. Your popular social site, your company’s site, commerce site, hobby site, site you install software from or even sites run by your government might be using vulnerable OpenSSL. Many of online services use TLS to both to identify themselves to you and to protect your privacy and transactions. You might have networked appliances with logins secured by this buggy implementation of the TLS. Furthermore you might have client side software on your computer that could expose the data from your computer if you connect to compromised services.

That point about networked appliances is particularly worrying. in the last two years a lot of devices (routers, switches, firewalls etc) may have shipped with embedded services built against vulnerable versions of the openssl library.

In my case alone I now have to generate new X509 certificates for all my webservers, my mail (both SMTP and POP/IMAP) services, and my openVPN services. I will also need to look critically at my ssh implementation and setup. I am lucky that I only have a small network.

My guess is that most professional sysadmins are having a very bad day today.

Permanent link to this article: http://baldric.net/2014/04/08/heartbleed/