Malicous and Suspicious Files – Finding and removing eval(base64_decode)

Are you keeping your Wordpress up-to-date ? What about the plugins you have ? What about the ones which are deactivated but still there ? We have a shared hosting and some of the wesites still ran on a old version of Wordpress with quite outdated plugin - perfect for testing your exploits. It happens that some the websites get “hacked” - usually they manage to upload a payload and run an php mailer or something simmilar. There are some easyer and quick ways to clean it when it comes to this point.

The original Article Written by Rahul Bansai can be found here


  • Command to list all infected files:
grep -lr --include=*.php "eval(base64_decode" /path/to/webroot

This is not necessary but its better to check some files manually to confirm if they have malicious code we are looking for. Also we can use this command after running cleanup command to crosscheck if cleanup is really successful.

  • Command to remove malicious code:

If above command gives you correct output, execute following command to perform actual cleaning:

grep -lr --include=*.php "eval(base64_decode" /path/to/webroot | xargs sed -i.bak 's/<?php eval(base64_decode[^;]*;/<?phpn/g'
  • Executing above will remove eval(*) codes. Above command will also generate a backup version of files it will modify. For example, if it removes code from index.php, you will find a new file index.php.bak in same directory with original content of index.php Now after running above command, you still find some more infected files, then you need to adjust search and replace parameters in for “sed” part. You may also use following command for a “liberal” cleaning at the risk of breaking something. (in case you really break something, like I did, you can jump to “Troubleshooting” section below!)
grep -lr --include=*.php "eval(base64_decode" /path/to/webroot | xargs sed -i.bak '/eval(base64_decode*/d'

Trying to avoid re-appearance of this code injection

Its really though to cover every possible way to protect yourself from such attach in this post.

If you remember, WordPress community faced this kind of issue because of WP-PhpMyAdmin plugin sometime back. In our case, we found some old WordPress demo sites were having that plugin installed.

To remove WP-PhpMyAdmin plugin form all WordPress sites on your server, execute following command:

find /path/to/webroot -name "wp-phpmyadmin" -type d | xargs rm -rf

Above is all we did to get rid of eval(base64_decode(*)) codes from all files on our test server. If this happens again on our server, I will update this post with added info.

Troubleshooting:

Just in case you end up in a mess, below are some useful commands.

  • Missing <?php tag in the beginning:

To add “<?php: tag in the beginning of index.php files, in case if you remove it accidentally use following command:

find /var/www/ -name "index.php" | grep "/htdocs/index.php" | xargs grep -L "<?php" | xargs sed -i "1s/^/<?php n/"

Don’t worry. If you already have a “<?php ” tag in the beginning, it won’t be added again.

  • Extra Newlines at the top!

If you find after cleanup, extra newlines at the top of your code, then use following command to remove trailing newlines. Extra newlines creates problem for blog feeds.

find . -name '\*.php' -exec sed -i -e :a -e '/^n\*$/{$d;N;ba' -e '}' '{}' ;