POODLE SSL 3.0 Vulnerability: What it is and how to deal with it

Posted: October 17th, 2014
Filed under: IIS & HTTP


 

from our friends at Net-Square

A Vulnerability known as POODLE, an acronym for Padding Oracle On Downgraded Legacy Encryption, is making headlines this week. The bug is a vulnerability in the design of SSL version 3.0, which is more than 15 years. However, SSL 3.0 is still widely supported, and nearly 97% of SSL servers are likely to be vulnerable to the bug, according to an October Netcraft Survey.

SSL v3.0 Vulnerable Servers

 

This vulnerability allows an attacker to intercept plaintext data from secure connections. Since SSLv3 has been quiet famous in the last 15 years it has put literally millions of browsers in jeopardy. As the chart above indicates, this is a vulnerability that has a sweeping impact.

How it happens?

Though users are upgrading to latest SSL versions (TLS 1.0, 1.1, 1.2), many TLS versions are backward compatible with SSL 3.0, hence when web browsers fail at connecting on these newer SSL version (i.e. TLS 1.0, 1.1, or 1.2), they may fall back to the older SSL 3.0 connection for a smooth user experience.

The other possibility is, a user is forced to step down to SSL 3.0. If an attacker has successfully performed a Man In The Middle attack MITM and causes connection failures, including the failure of TLS 1.0/1.1/1.2 connections. They can force the use of SSL 3.0 and then exploit the poodle bug in order to decrypt secure content transmitted between a server and a browser. Due to this down shift of the protocol the connection becomes vulnerable to the attack, eventually exploiting and intercepting user’s private data.

Google’s Bodo Möller, Thai Duong, and Krzysztof Kotowicz published the complete security advisory which can be found on openssl.org.

Possible remediation

To avoid falling prey to attackers exploiting POODLE, avoiding the use of public Wi-Fi hotspots, if user is sending valuable information (using online banking, accessing social networks via a browser, etc.), and noting this is always a risk, but the Poodle vulnerability makes it even more dangerous.

The other recommendation is disabling SSL v3 and all previous versions of the protocol in your browser settings and also on the server side will completely avoid it.  SSL v3 is 15 years old now and has been superseded by the more up-to-date and widely supported TSL protocol, supported by most modern web browsers.

DigitCert published a detailed step-by-step guide for disabling SSL 3.0.

Richard Burte also shared the command lines to disable SSL 3.0 on GitHub.

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