Roundcube 1.6.14 won't save uploaded images in signatures

Symptoms

After uploading an image into a Roundcube signature block, the image will be removed when the signature is saved.

Description

New security checks were introduced in Roundcube version 1.6.14 that inadvertently remove base64 images from signature blocks.

We've opened an internal case for our development team to investigate this further. For reference, the case number is CPANEL-52289. Follow this article to receive an email notification when a solution is published in the product. 

Workaround

1. Access the server's command line as the 'root' user via SSH or "Terminal" in WHM.
2. Open /usr/local/cpanel/base/3rdparty/roundcube/program/lib/Roundcube/rcube_washtml.php in your preferred text editor.
3. Scroll down to line 431.

4. Add an equal sign = just before the plus sign + in the preg_match check.

   if (stripos($type, 'base64') === false || preg_match('|[^0-9a-z\s/=+]|i', $matches[2])) {

5. Save the changes and close the editor.