Secure transmission of data requires encrypting the data in many ways. Ciphers are the tools used for data encryption. RC4 is one such cipher.

RC4 generates a stream of pseudo-random bits. These bits are combined with plain text using ‘bit-wise exclusive-or’ pattern to produce the encrypted message, which is transmitted in TLS connections.

In 2011, when BEAST attack was revealed, RC4 cipher was unaffected by it. As a result, RC4 ciphers started to be used widely in TLS encryption protocol.

Is RC4 cipher secure?

However, this stability didn’t last long. In 2013, a new set of attacks were revealed, which could easily obtain plain text from the RC4 encrypted messages.

In 2015, a ‘NOMORE’ attack against RC4 ciphers was revealed. Using this attack, it was possible to decrypt a secure HTTP cookie within a few hours.

As a result, it was crucial to disable RC4 ciphers in the TLS configuration of the web servers, to protect the confidential information from being leaked.

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How to disable RC4 ciphers?

In our previous post, we’ve discussed how to disable insecure protocols SSLv2 and SSLv3. Today we’ll see how to disable the weak RC4 cipher in cPanel/WHM servers.

We strongly recommend to use only strong ciphers for our customers’ web servers. To update this, go to WHM. The option to choose is:

• Home » Service Configuration » Apache Configuration » Global Configuration

  In the ‘SSL Cipher Suite’ section, enter the CipherSuite:

ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:AES:CAMELLIA:DES-CBC3-SHA:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK:!aECDH:!EDH-DSS-DES-CBC3-SHA:!EDH-RSA-DES-CBC3-SHA:!KRB5-DES-CBC3-SHA 

In this setting, only the strong Ciphers are enabled and weak ciphers like RC4 are disabled by using a ! symbol.

Disable RC4 cipher in cPanel/WHM server

Save the changes, Rebuild configuration and Restart apache, for the changes to take into effect. For the latest versions of cPanel/WHM, this cipher is enabled by default.

Some web servers require all Ciphers to be enabled by default. In such servers, we disable the weak ciphers such as RC4 and enable everything else by default.

The ‘SSL Cipher Suite’ in those servers would be similar to:

ALL:!ADH:!RC4:+HIGH:+MEDIUM:-LOW:-SSLv2:-EXP:!kEDH

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In short..

If not configured properly, encrypted communications can be broken quite easily. Our 24/7 security team alerts us promptly when a vulnerability occurs.

RC4 and other weak ciphers are disabled for other cPanel/WHM services such as Exim, IMAP, POP, etc. in the servers that we manage.

Timely alerts enable us to apply the patches in our customers’ servers before a hack occurs. We also implement secure TLS/SSL measures in the servers to maintain them secure.

Bobcares helps online businesses of all sizes achieve world-class security and uptime, using tried and tested solutions. If you’d like to know how to make your server more reliable, we’d be happy to talk to you.