Poodle image via Flickr
, CC license
For the last week we've been tracking rumors about a new vulnerability in SSL. This specific vulnerability,
which was just announced
, targets SSLv3. 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 which dubs the bug POODLE (
PDF
).
Generally, modern browsers will default to a more modern encryption protocol (e.g., TLSv1.2). However, it's possible for an attacker to simulate conditions in many browsers that will cause them to fall back to SSLv3. The risk from this vulnerability is that if an attacker could force a downgrade to SSLv3 then any traffic exchanged over an encrypted connection using that protocol could be intercepted and read.
In response, CloudFlare has disabled SSLv3 across our network by default for all customers. This will have an impact on some older browsers, resulting in an SSL connection error. The biggest impact is Internet Explorer 6 running on Windows XP or older. To quantify this, we've been tracking SSLv3 usage.
SSLv3 Usage Stats
Across our network, 0.09% of all traffic is SSLv3. For HTTPS traffic, 0.65% across our 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.
