The eval(base64_decode) virus attack in wordpress

Last day, it came into my notice that our FOSS website, foss.amrita.ac.in gets redirected to some .uk malicious websites, when external links were clicked from websites like Facebook, Google. I was going through the wp-admin->Edit Theme files and it came to my notice that the entire files were infected by a virus which encoded some php code in base_64 encryption.

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On decoding, I found that it was responsible for all those malicious redirects.
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How to remove it:-

  1. Disable all plugins and delete all the unwanted plugin files from wp-content/plugins
  2. Inorder to find which all files got infected, run a ‘ grep -r base64 *’ under the wp-content folder via ssh or ftp access
  3. Delete all plugin folder’s which will have the malicious code, for me it was inside a particular plugin, which I removed later to clear all issues.
  4. Reinstall the theme files again.
  5. Share the website link on facebook, try clicking on it again.

What to be taken care of :-

  1. Never leave any file permission above 755. Feel free to give 755 or 754 to folders in wp-content/plugins or wp-content/themes.
  2. Make sure that the file permission of wp-config.php is 600.
  3. Never install unpopular plugins or themes.
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