Php-Malware-Finder - Detect Potentially Malicious PHP Files

PHP-malware-finder does its very best to detect obfuscated/dodgy code as well as files using PHP functions often used in malwares/webshells.

The following list of encoders/obfuscators/webshells are also detected:

Bantam Best PHP Obfuscator Carbylamine Cipher Design Cyklodev Joes Web Tools Obfuscator P.A.S PHP Jiami Php Obfuscator Encode SpinObf Weevely3 atomiku cobra obfuscator nano novahot phpencode tennc web-malware-collection webtoolsvn

Of course it's trivial to bypass PMF, but its goal is to catch kiddies and idiots, not people with a working brain. If you report a stupid tailored bypass for PMF, you likely belong to one (or both) category, and should re-read the previous statement.

How does it work?

Detection is performed by crawling the filesystem and testing files against a set of YARA rules. Yes, it's that simple!

Instead of using an hash-based approach, PMF tries as much as possible to use semantic patterns, to detect things like "a $_GET variable is decoded two times, unzipped, and then passed to some dangerous function like system".

Installation

Install Yara.
This is also possible via some Linux package managers: Debian: sudo apt-get install yara Red Hat: yum install yara (requires the EPEL repository)

You can also compile it from source:

Download php-malware-finder git clone https://github.com/jvoisin/php-malware-finder.git

How to use it?

Or if you prefer to use yara:

Please keep in mind that you should use at least YARA 3.4 because we're using hashes for the whitelist system, and greedy regexps. Please note that if you plan to build yara from sources, libssl-dev must be installed on your system in order to have support for hashes.

Oh, and by the way, you can run the comprehensive testsuite with make tests.

Whitelisting

Check the whitelist.yar file. If you're lazy, you can generate whitelists for entire folders with the generate_whitelist.py script.

Why should I use it instead of something else?

Because:

It doesn't use a single rule per sample, since it only cares about finding malicious patterns, not specific webshells It has a complete testsuite, to avoid regressions Its whitelist system doesn't rely on filenames It doesn't rely on (slow) entropy computation It uses a ghetto-style static analysis, instead of relying on file hashes Thanks to the aforementioned pseudo-static analysis, it works (especially) well on obfuscated files

Licensing

PHP-malware-finder is licensed under the GNU Lesser General Public License v3.

The amazing YARA project is licensed under the Apache v2.0 license.

Patches, whitelists or samples are of course more than welcome.