A major vulnerability affecting the security of cloud services dubbed POODLE (Padding Oracle on Downgraded Legacy Encryption) was reported on October 14th by three Google security researchers—Bodo Moller, Thai Duong, and Krzysztof Kotowicz. Their paper about the vulnerability is available here.
What is POODLE?
POODLE affects SSLv3 or version 3 of the Secure Sockets Layer protocol, which is used to encrypt traffic between a browser and a web site or between a user’s email client and mail server. It’s not as serious as the recent Heartbleed and Shellshock vulnerabilities, but POODLE could allow an attacker to hijack and decrypt the session cookie that identifies you to a service like Twitter or Google, and then take over your accounts without needing your password.
This vulnerability allows for the hijacking and decryption of SSL version 3.0 connections, which is used to encrypt traffic between a browser and a web site or between a user’s email client and mail server. While usage of SSL 3.0 is generally limited, there is still prevalent backward-compatibility support of the protocol that exposes nearly all browsers and users.
The SSLv3 protocol has been in use since its publication in 1996. TLSv1 was introduced in 1999 to address weaknesses in SSLv3, notably introducing protections against CBC (Cipher block chaining) attacks. Although SSLv3 is considered a legacy protocol, it is still commonly permitted for backward compatibility by the default configurations of many web servers including Apache HTTP Server and Nginx. Many browsers’ support will fall back to the use of SSLv3 if an HTTPS connection to a server doesn’t support the TLSv1 protocol or a TLSv1 protocol negotiation fails for any reason.
What’s the risk?
The danger arising from the POODLE attack is that a malicious actor with control of an HTTPS server or some part of the intervening network can cause an HTTPS connection to downgrade to the SSLv3 protocol. An attack against SSLv3’s CBC encryption schemes can then be used to begin decrypting the contents of the session. Essentially, POODLE could allow an attacker to hijack and decrypt the session cookie that identifies a cloud service user to a service like Twitter or Google, and then take over your accounts without needing your password.
How to protect your company’s data
We recommend disabling the SSLv3 protocol on all servers, relying only on TLSv1.0 or greater. Additionally, company browsers and forward proxies should disallow SSLv3 and likewise permit only TLSv1.0 or greater as a minimum SSL protocol version. Enterprises should also disable the use of CBC-mode ciphers. To patch retrying of failed connections, apply TLS_FALLBACK_SCSV option (e.g. http://marc.info/?l=openssl- dev&m=141333049205629&w=2).
Legacy applications relying solely on SSLv3 should be considered at-risk and vulnerable. Generic encryption wrapper software like Stunnel can be used as a workaround to provide encrypted TLSv1 tunnels.
How many cloud services are vulnerable?
As of this morning, 61% of cloud services had not addressed the Poodle vulnerability with a fix. The fact that many cloud services still support SSLv3 is a sign that cloud providers are not paying attention to what protocols are offered by their SSL stack. Cloud service providers should start looking at their SSL stack configuration and make sure they have disabled previous versions of SSLv3. In the process, they should also ensure the SSL stack’s proper use of ciphers.
We are working with customers to proactively identify vulnerable services and users and provide guidance for measures required to protect their data and user accounts. To learn more about our recommendations for securing data in the cloud, download our cheat sheet below.