It’s been a while since I checked on the status of PHP malware versus anti-virus. So, here is a quick catch up post. (I’ve been talking about this for a while now. Here is an old example.)
I took a randomly selected piece of PHP malware from the HITME and checked it out this afternoon. Much to my surprise, the malware detection via AV has gotten better.
The malware I grabbed for the test turned out to be a multi-stage PHP backdoor. The scanner thought it was exploiting a vulnerable WordPress installation.
I unpacked the malware parts into plain text and presented both the original packed version from the log and the unpacked version to VirusTotal for detection testing. As you know, in the past, detection of malware PHP was sub single digits in many cases. That, at least to some extent has changed. For those interested, here are the links to see what was tripped.
Decoded to plain text vs Encoded, as received
As you can see, decoded to plain text scored a detection of 44% (19/43), which is significantly improved from a year or so ago. Additionally, excitingly, undecoded, the attack in raw form triggered a detection rate of 30% (13/44)! The undecoded result is HUGE, given that the same test a year or so ago often yielded 0-2% detection rates. So, it’s getting better, just SLOWLY.
Sadly though, even with the improvements, we are still well below half (50%) detection rates and many of the AV solutions that fail to catch the PHP malware are big name vendors with commercial products that organizations running PHP in commercial environments would likely be depending on. Is your AV in the missing zone? If so, you might want to consider other forms of more nuanced detection.
Now, obviously, organizations aren’t just depending on AV alone for detection of web malware. But, many may be. In fact, a quick search for the dropped backdoor file on Google showed 58,800 systems with the dropped page name (a semi-unique indicator of compromise). With that many targets already victim to this single variant of PHP backdoors, it might be worth checking into if you are a corporate PHP user.
Until next time, take a look around for PHP in your organization. It is a commonly missed item in the patch and update cycles. It also has a pretty wide security posture with a long list of known attack tools and common vulnerabilities in the coding patterns used by many popular products. Give any PHP servers you have a deeper inspection and consider adding more detection capability around them. As always, thanks for reading and stay safe out there!
