Engineers at Google found a new vulnerability in SSL version 3.0 (SSLv3) and they call it POODLE (Padding Oracle On Downgraded Legacy Encryption). The vulnerability allows an attacker to add padding to a request in order to then calculate the plaintext of encryption using the SSLv3 protocol. Effectively, this allows an attacker to compromise the encryption when using the SSLv3 protocol. Full details have been published by Google in a paper.
Who does this affect?
SSLv3 is nearly 15 years old, but support for it remains widespread. Most importantly, nearly all browsers support it and, in order to work around bugs in HTTPS servers, browsers will retry failed connections with older protocol versions, including SSL 3.0. Because a network attacker can cause connection failures, they can trigger the use of SSL 3.0 and then exploit this issue.
However, the only group of users who will be seriously affected by this bug is those who are still using Internet Explorer 6 on Windows XP (both are already at their End of Life).
According to CloudFlare, 0.09% of all traffic across their network is SSLv3. For HTTPS traffic, 0.65% across their network uses SSLv3. The good news is most of that traffic is actually attack traffic and some minor crawlers. For real visitor traffic, today 3.12% of CloudFlare’s total SSL traffic comes from Windows XP users. Of that, 1.12% Windows XP users connected using SSLv3. In other words, even on an out-of-date operating system, 98.88% Windows XP users connected using TLSv1.0+ — which is not vulnerable to this vulnerability.
We will be disabling SSLv3 across all of our servers as this is a serious vulnerability with no patch in sight (as SSLv3 is very old) and most web browsers will be dropping support for SSLv3 after this POODLE incident anyway.
If you receive any complaints from your website visitors who are affected by the decision to disable SSLv3, we highly recommend that you suggest them to stop using Internet Explorer 6 and switch to a modern browser like Google Chrome, Mozilla Firefox, Safari and Opera.
For those of you who are not aware, even Microsoft is discouraging Windows XP users from using Internet Explorer 6 with their IE 6 Countdown website since the year 2011.
(Poodle image via Flickr, CC license.)