What is CCS Injection, and how to prevent it?

In this article:

The ChangeCipherSpec (CCS) injection vulnerability affects certain versions of OpenSSL. Here’s what you need to know about it.

CCS Injection Security Assessment

Security Assessment Prevent CCS Injection


What is a CCS injection vulnerability?

The CCS injection vulnerability (CVE-2014-0224) is an OpenSSL vulnerability that was discovered in 2014. It affects OpenSSL versions 0.9.8, 1.0.0, and 1.0.1 and is not an SSL or TLS specification issue.

The vulnerability affects the ChangeCipherSpec request message in these older OpenSSL versions and opens the door for a man-in-the-middle attack (MITM). A MITM allows an attacker to intercept, decrypt and even modify the data exchanged between clients and servers. This would allow them to hijack a session, corrupt data, or obtain sensitive information. 

To pose a real threat, the vulnerability must be present both on the client and server sides. A CCS injection cannot be performed if only one party is vulnerable. While this makes a CCS injection less likely, it does not eliminate the threat entirely, and the best measure is to apply a patch.

How does the CCS injection take place?

To be successful, this type of injection relies on a vulnerability that arises during the session initiation of SSL/TLS connections in the affected OpenSSL versions. 

Typically, sessions begin with handshake messages between client and server. At this stage, the connection parameters are negotiated, including which SSL/TLS version will be used and which cipher/encryption protocol and encryption keys will be exchanged, along with the Message Authentication Code (MAC) and more.

During this process, the cipher may be renegotiated after it has already been agreed upon by either the server or the client using the ChangeCipherSpec (CCS) request. When sent by either party, this triggers a shift to a different set of ciphers and signals that anything exchanged after that will be protected using the ciphers and keys that have been renegotiated. This whole process occurs during the handshake stage. 

However, with the vulnerable OpenSSL versions, the CCS could be sent prior to the initial negotiation of the cipher and other security parameters. This would lead to desynchronization due to the CCS request breaking the standard order of the talks. Without a vulnerability, such desynchronization would lead to the connection attempt being terminated. 

As part of the CSS injection, man-in-the-middle attackers could interfere with the handshake parameters by sending a CSS request to the server and the client. This made the vulnerable versions issue and used a pre-master secret key with zero length. Based on this zero-length pre-master key, session keys are agreed upon, effectively breaking the encryption of the session and making it vulnerable. This would allow attackers to eavesdrop, decrypt, and modify data being exchanged. 

OpenSSL addressed this vulnerability by changing how CCS requests were handled and making it impossible to use zero-length master keys, effectively disabling the exposure. Moreover, it was also made impossible for CCS messages to be accepted before the initial cipher and key negotiation.

What is the impact of the CCS injection?

Unlike other injection attacks, the CCS injection cannot be used to extract data from clients and servers. This means that any data stored on either side is safe. However, if the injection is successful, it allows attackers to capture and decrypt packets in transit between parties. 

I.e., such an injection could potentially expose or corrupt sensitive data. This includes authentication and session details, allowing attackers to hijack a session. It could also include personal financial or health data, sensitive communications, etc.  

Prevention Guide for SSL/TLS Vulnerabilities

Prevention Guide

Learn how to detect and prevent different kinds of SSL/TLS vulnerabilities.


How to fix the CCS injection vulnerability?

The best way to fix the CCS injection vulnerability is to update OpenSSL to the latest version available. 

Versions that addressed the CCS injection vulnerability were 0.9.8za, 1.0.0m, and 1.0.1h. However, all these versions are already considered old and are not maintained, so it is better to update the latest versions currently being used and supported.

E.g., run:

apt-get update; apt-get upgrade # Debian / Ubuntu
yum update                      # RHeL / CentOS
pacman -Syu                     # Arch Linux

There is no known way to mitigate this issue without an update.


Is the CCS injection the same as HeartBleed?

No, the CCS injection and the HeartBleed bug are two types of OpenSSL vulnerabilities that differ in scope and impact.

Do certificates need to be regenerated if this vulnerability is found?

No, this is unnecessary since the vulnerability does not lead to a certificate or private key leak. It is only necessary to update OpenSSL to the latest available version.

Can the CCS injection vulnerability be fixed without an update?

There are no known ways to avoid this vulnerability without applying an update.

Has the CCS injection vulnerability ever been exploited in the wild?

It is not known for this attack to have been conducted successfully in the wild.

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