POODLE Attack

C.

A flaw was found in the way SSL 3.0 handled padding bytes when decrypting messages encrypted using block ciphers in cipher block chaining (CBC) mode.

How To Protect your Server Against the POODLE SSLv3 Vulnerability On October 14th, 2014, a vulnerability in version 3 of the SSL encryption protocol was disclosed.

This vulnerability, dubbed POODLE (Padding Oracle On Downgraded Legacy Encryption), allows an attacker to read information encrypted with this version of the protocol in plain text using a man-in-the-middle attack.

Although SSLv3 is an older version of the protocol which is mainly obsolete, many pieces of software still fall back on SSLv3 if better encryption options are not available.

More importantly, it is possible for an attacker to force SSLv3 connections if it is an available alternative for both participants attempting a connection.

The POODLE vulnerability affects any services or clients that make it possible to communicate using SSLv3

Because this is a flaw with the protocol design, and not an implementation issue, every piece of software that uses SSLv3 is vulnerable.

To find out more information about the vulnerability, consult the CVE information found at CVE-2014-3566

What is the POODLE Vulnerability? The POODLE vulnerability is a weakness in version 3 of the SSL protocol that allows an attacker in a man-in- the-middle context to decipher the plain text content of an SSLv3 encrypted message.

Who is Affected by this Vulnerability? This vulnerability affects every piece of software that can be coerced into communicating with SSLv3

This means that any software that implements a fallback mechanism that includes SSLv3 support is vulnerable and can be exploited.

Some common pieces of software that may be affected are web browsers, web servers, VPN servers, mail servers, etc.

How Does It Work? In short, the POODLE vulnerability exists because the SSLv3 protocol does not adequately check the padding bytes that are sent with encrypted messages.

Since these cannot be verified by the receiving party, an attacker can replace these and pass them on to the intended destination.

When done in a specific way, the modified payload will potentially be accepted by the recipient without complaint.

An average of once out of every 256 requests will accepted at the destination, allowing the attacker to decrypt a single byte.

This can be repeated easily in order to progressively decrypt additional bytes.

Any attacker able to repeatedly force a participant to resend data using this protocol can break the encryption in a very short amount of time.

How Can I Protect Myself? Actions should be taken to ensure that you are not vulnerable in your roles as both a client and a server.

Since encryption is usually negotiated between clients and servers, it is an issue that involves both parties.

Servers and clients should should take steps to disable SSLv3 support completely.

Many applications use better encryption by default, but implement SSLv3 support as a fallback option.

This should be disabled, as a malicious user can force SSLv3 communication if both participants allow it as an acceptable method.

The POODLE (Padding Oracle On Downgraded Legacy Encryption) attack is a type of Man-in-the-Middle (MITM) exploit that targets SSLv3.0 protocol with Cipher Block Chaining (CBC) mode. The attack takes advantage of a vulnerability in the SSLv3.0 protocol that allows an attacker to decrypt the encrypted messages exchanged between a client and a server.

To carry out the attack, the attacker first intercepts the communication between the client and server and downgrades the encryption protocol to SSLv3.0. The attacker then exploits a flaw in the CBC mode of encryption, where they can manipulate the padding in the final block of the cipher to reveal one byte of plaintext at a time. By repeating this process, the attacker can decrypt the entire message.

TLS1.0 with CBC mode cipher is also vulnerable to the POODLE attack, but SSLv2.0 and SSLv3.0 with ECB mode cipher are not affected. Therefore, the correct answer is C. SSLv3.0 with CBC mode cipher.

It's important to note that the SSLv3.0 protocol is now considered insecure and has been replaced by newer and more secure protocols such as TLS 1.2 and TLS 1.3. Most modern web browsers and servers no longer support SSLv3.0, and it is recommended to disable SSLv3.0 on any systems that still use it.