Backdoors are pieces of code that allow attackers to bypass authentication, maintain their access to the server and reinfect files. Some of those malicious files can be as simple as a single line of code, allowing the execution of remote code, or complex algorithms, providing different functions to the attacker.
This is detection of malicious files with common hex -> xor obfuscation. This means that the final payload code is divided into two or more parts which are xored and moreover, the these parts are in form of hexadecimal character representation.
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Any PHP based web site (often through outdated WordPress, Joomla, osCommerce, Magento, Drupal and stolen passwords).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.
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Dump
Part of a malicious script using the hex -> xor function:
IPwXsveV='p'. 'reg_replac'.'e'; $ivAqSMVn="rbjfxy6ilF1hhrbHIo3"^"\x5d\x1b\x22\x02\x283c9\x2b3y\x0c...