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SSLv3 Disabled Due to POODLE Vulnerability

October 26, 2014

Security researchers at Google recently announced their discovery of a flaw in Version 3 of the SSL protocol ("SSLv3"). The attack, called POODLE ("Padding Oracle On Downgraded Legacy Encryption"), can be exploited by attackers who are able to modify network transmissions between the browser and the server. A successful attack can result in, for example, an attacker being able to read the cookies sent by a browser over an SSL (HTTPS) request.

Vulnerability Details

To perform the attack, an attacker must have both

  1. a way to force the browser to make SSL requests, and
  2. the ability to modify network traffic between the browser and the server.

The attack starts by convincing the browser to make SSL requests to an SSL-enabled website that supports SSLv3. This could be done, for example, by an attacker who is in control of the network inserting JavaScript into the HTML response from a website that is served over plain HTTP.

Next, the attacker, who must be able to modify network traffic (for example, they are in control of a router between the browser and server), interferes with the SSL handshake to convince both the browser and the server to use the SSLv3 protocol instead of a newer TLS protocol.

Finally, over a period of requests (possibly around 256 requests for each byte the attacker needs to decrypt), the attacker uses cryptographic flaws in ciphers supported by SSLv3 to decrypt transmitted data.

What We Have Done

We have updated all of our users' servers with a patched version of Nginx that disables default support for SSLv3.

What You Should Do

No further action is required by you. Your servers do not require a reboot.

If you believe you need support for SSLv3, please contact us and we can discuss the situation with you and provide you instructions on how to enable SSLv3 on your servers.