The SSLv3 “POODLE” Vulnerability.
Most of us are aware of the recent protocol flaw vulnerability in SSLv3. Officially designated CVE-2014-3566, it is more commonly referred to as the “POODLE” (Padding Oracle On Downgraded Legacy Encryption) vulnerability.
The vulnerability is a result of a flaw in the way that the (now old) SSLv3 protocol behaves and operates. There is a Ubuntu-specific question on the POODLE vulnerability on Ask Ubuntu (link) which answers common questions on it. There is also a more general question on the POODLE vulnerability on the Information Security Stack Exchange site (link) with more general details on the POODLE vulnerability. If you would like more details, you should refer to those sites, or read the OpenSSL Whitepaper on the POODLE vulnerability (link).
As this is a protocol flaw in SSLv3, ALL implementations of SSLv3 are affected, so the only way to truly protect against POODLE is to disable SSLv3 protocol support in your web application, whether it be software you write, or hosted by a web server.
Disable SSLv3 in
Since the recommendation is to no longer use SSLv3, the simplest thing to do is disable SSLv3 for your site. In
nginx, this is very simple to achieve.
Typically, one would have SSL enabled on their site with the following protocols line or similar if using the example in the default-shipped configuration files (in latest Debian or the NGINX PPAs, prior to the latest updates that happened in the past week or so):
ssl_protocols SSLv3 TLSv1 TLSv1.1 TLSv1.2;
To resolve this issue and disable SSLv3 support, we merely need to use the following instead to use only TLS:
ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
Note that on really old implementations of OpenSSL, you won’t be able to get TLSv1.1 and TLSv1.2, so at the very least you can just have TLSv1 on the
ssl_protocols line. You should probably consider updating to a more recent version of OpenSSL, though, because of other risks/issues in OpenSSL.
Update OpenSSL to get
More importantly than just disabling SSLv3, you should definitely update your OpenSSL, or whatever SSL implementation you use, to receive support for
TLS_FALLBACK_SCSV. There is an attack vector that would make you vulnerable to POODLE by starting a TLS session, but then falling back to SSLv3, and then open you to the POODLE vulnerability. By updating, and then having the use of
TLS_FALLBACK_SCSV, you will be protecting yourself from protocol downgrading attacks which would also make you vulnerable to POODLE.
Fortunately for all users of Ubuntu, the OpenSSL packages were updated to protect against SSL downgrade attacks. This is detailed in “USN-2385-1: OpenSSL vulnerabilities” (link). Simply running
sudo apt-get update with the security repositories enabled should get you the OpenSSL update to address this.
nginx from the Ubuntu Repositories:
Due to the vulnerability, and Debian already having these changes done, I was able to get in a last-minute update (courtesy of the Ubuntu Security Team and the Ubuntu Release Team), into the nginx package for the Utopic (14.10) release, which happened officially yesterday (October 23, 2014). In Utopic, the
nginx package’s default config does NOT have SSLv3 on the
ssl_protocols line. All other supported versions of Ubuntu do not have this change (this means that Precise and Trusty are both affected).
Of course, many users of Ubuntu and
nginx like the newer features of the latest nginx Stable or Mainline releases. This is why the
nginx PPAs exist. Originally maintained by some of the Debian maintainers of the nginx package, I’ve taken primary responsibility of updating the nginx packages, and keeping them in sync (as close as I can) to the Debian
As of today (October 24, 2014), both the Stable and Mainline PPAs have been updated to be in sync with the latest Debian packaging of the nginx package. This includes the removal of
SSLv3 from the default
Fortunately, like Ubuntu, Debian has also updated the OpenSSL packages to protect against SSL downgrade attacks. This is detailed in “DSA-3053-1 openssl — security update” (link). Like in Ubuntu, this can be fixed by running
sudo apt-get update or similar to update your packages.
nginx in the Debian Repositories:
If you are on Debian Unstable, you are in luck. The Debian package in Unstable has this change in it already.
If you are on Debian Testing or Debian Stable or Debian Old Stable, you’re unfortunately out of luck, this change isn’t in those versions of the package yet. You can easily do the aforementioned changes, though, and fix your configs to disable SSLv3.