POODLE Attack - Time to die for SSL 3.0

Exploiting SSL 3.0 - The POODLE Attack

On 14th Oct,2014 google has published a serious vulnerability in blueprint of SSL 3.0,naming POODLE – short for Padding Oracle On Downgraded Legacy Encryption. This flaw is not a software bug. This vulnerability allows attackers to decrypt the encrypted sessions between website server and client.

As per Alexa 542,902 sites are SSL 3.0 supported which is 96.9% of HTTPS Alexa.

Exploiting this vulnerability can result in compromise of cookies leading account hijacks. As informed the attack is easy to perform but attacker should be able to capture the traffic. It affects all browsers supporting SSL 3.0 Google Chrome, Mozila Firefox and IE etc.

 The attacker can cause connection failure and forcing the browser to use SSL 3.0 or CBC-mode ciphers with SSL 3.0 and exploiting the vulnerability. So to mitigate this vulnerability is simply disable SSL 3.0 but you may face some compatibility issue. Google has recommended use of TLS_FALLBACK_SCSV

 the Transport Layer Security Signalling Cipher Suite Value that blocks protocol downgrades. This prevent the future downgrade attacks.

To work with legacy servers, many TLS clients implement a downgrade dance: in a first handshake attempt, offer the highest protocol version supported by the client; if this handshake fails, retry (possibly repeatedly) with earlier protocol versions. Unlike proper protocol version negotiation (if the client offers TLS 1.2, the server may respond with, say, TLS 1.0), this downgrade can also be triggered by network glitches, or by active attackers. So if an attacker that controls the network between the client and the server interferes with any attempted handshake offering TLS 1.0 or later, such clients will readily confine themselves to SSL 3.0.

A Detailed guide to POODLE attack can be found here

Countermeasures / Remediation:

Server-Side Countermeasures

Disabling SSL 3.0 in nginx

Disabling the SSL 3.0 in nginx can be done by giving instructions to use only TLS.

change the ssl_protocols Directive or if ssl_protocol directive is not present then mention it on top of configuration file.

ssl_protocols TLSv1 TLSv1.1 TLSv1.2;

Disabling SSL 3.0 in Apache

For httpd version 2.2.23 and newer change SSL configuration file.add TLSv1, TLSv1.1, and TLSv1.2.

SSLProtocol +TLSv1 +TLSv1.1 +TLSv1.2 

For httpd version 2.2.22 and older, only specify TLSv1, It will treat it as a wildcard for all TLS versions.

SSLProtocol TLSv1

Client-Side Countermeasures

Firefox

Please refer here for more info.

Google Chrome

1) Create a Chrome shortcut on desktop and right click.

2) Click on properties

3 )Click on shortcut tab

4)Edit the 'Target' textbox and add double quotes in last (")

5) type --ssl-version-min=tls1

6) Click "OK"

7) You will be asked for Admin permissions, click "Continue"

NOTE: Above steps will work only when you use chrome from desktop shortcut

Internet Explorer

To disable SSLv3 in IE, uncheck the "Use SSL 3.0" box on the "Advanced" tab in the Internet Options program

1) Launch "Internet Options" from the Start Menu

2) Click the "Advanced" tab

3) Uncheck "Use SSL 3.0"

4) Click "OK"