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Friday, October 24, 2014

SSLv3 POODLE Vulnerability - How To Secure Your Windows Client/Server

The POODLE vulnerability is an attack on the SSL 3.0 protocol and it’s a protocol flaw not an implementation issue.

Description From US-CERT.GOV Website

The SSL 3.0 vulnerability stems from the way blocks of data are encrypted under a specific type of encryption algorithm within the SSL protocol. The POODLE attack takes advantage of the protocol version negotiation feature built into SSL/TLS to force the use of SSL 3.0 and then leverages this new vulnerability to decrypt select content within the SSL session. The decryption is done byte by byte and will generate a large number of connections between the client and server.

While SSL 3.0 is an old encryption standard and has generally been replaced by Transport Layer Security (TLS) (which is not vulnerable in this way), most SSL/TLS implementations remain backwards compatible with SSL 3.0 to interoperate with legacy systems in the interest of a smooth user experience. Even if a client and server both support a version of TLS the SSL/TLS protocol suite allows for protocol version negotiation (being referred to as the “downgrade dance” in other reporting). The POODLE attack leverages the fact that when a secure connection attempt fails, servers will fall back to older protocols such as SSL 3.0. An attacker who can trigger a connection failure can then force the use of SSL 3.0 and attempt the new attack.

Two other conditions must be met to successfully execute the POODLE attack: 1) the attacker must be able to control portions of the client side of the SSL connection (varying the length of the input) and 2) the attacker must have visibility of the resulting ciphertext. The most common way to achieve these conditions would be to act as Man-in-the-Middle (MITM), requiring a whole separate form of attack to establish that level of access.

These conditions make successful exploitation somewhat difficult. Environments that are already at above-average risk for MITM attacks (such as public WiFi) remove some of those challenges. 

Impact

The POODLE attack can be used against any system or application that supports SSL 3.0 with CBC mode ciphers. This affects most current browsers and websites, but also includes any software that either references a vulnerable SSL/TLS library (e.g. OpenSSL) or implements the SSL/TLS protocol suite itself. By exploiting this vulnerability in a likely web-based scenario, an attacker can gain access to sensitive data passed within the encrypted web session, such as passwords, cookies and other authentication tokens that can then be used to gain more complete access to a website (impersonating that user, accessing database content, etc.).

Solution For Microsoft Windows Server/IIS

Step 1

Step 1

Run Regedit as Administrator and navigate to:HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\Schannel\Protocols\
Step 2

Step 2

Right click Protocols and select New > Key option.
Step 3

Step 3

Name the new key as SSL 3.0.
Step 4

Step 4

Right click SSL 3.0 and create a new key named Client.
Step 5

Step 5

right click SSL 3.0 and create the key Server.
Step 6

Step 6

Right click Client and select New > DWORD (32bit) Value option.
Step 7

Step 7

Name the DWORD as DisabledByDefault. Double click the DWORD and type 1 as Value data then click OK to confirm.
Step 8

Step 8

The DWORD Value Data set to 1.
Step 9

Step 9

Repeat same procedure for Server and assign Enabled as a DWORD name. Leave default Value Data set to 0.

 

Once completed the above steps, you must reboot your server for the changes to take effect. If you are a managed hostedappliance.net customer and don't feel confident modifying registry, please contact our customer support and we will make necessary changes for you.

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