Ninety-Five Percent of Webshell Attacks Written in PHP

There’s nothing inherently malicious about a webshell, which is a script that can be uploaded to a web server to enable remote administration of the machine. In the hands of an attacker, however, they are a serious cyberthreat. Advanced persistent threat (APT) groups often use webshells to breach organizations.

Webshell Attacks Surging

Earlier this year, we reported on two notable upticks in webshell attacks: C99 Shell and b374k. This activity intrigued our analysts, warranting further investigation.

Our subsequent analysis of IBM Managed Security Services (MSS) data showed an increase in webshell attacks this year, most notably in Q2 and the beginning of Q3. We expect to see that trend continue in 2017.

graph of webshell attacks from Sept 2016 to Sept 2016.

PHP Is Prevalent and Persistent

Almost all the attacks — approximately 95 percent — were written in PHP, a widely used open-source scripting language. Although not readily apparent, the number of command injection attacks resulting from malicious PHP webshells is relatively significant. No other single command injection attack type was observed to be as prevalent, or as persistent, for as long.

Read the X-Force Research Report: Understanding the Webshell Game

Analysis of IBM MSS data from 2016 also revealed over 120 unique types of PHP webshell scripts. The great majority were observed in attempts to plant webshell scripts in remote servers via command injection to ultimately breach the servers and gain unauthorized access to the data they host. C99 was the most common variety, accounting for nearly 9 percent of the attacks recorded in 2016.

Malicious webshell exploitation is one of the easiest ways attackers can gain unauthorized access to an organization’s network. To learn about more about this threat, including ways to protect against it, read the IBM report titled “Understanding the Webshell Game.”

Share this Article:
Dave McMillen

Senior Threat Researcher, IBM Managed Security Services

Dave brings over 25 years of network security knowledge to IBM. Dave began his career in IBM over 15 years ago where he was part of a core team of six IBMers that created the IBM Emergency Response Service which eventually grew and evolved into Internet Security Systems.As an industry-recognized security expert and thought leader, Dave's background in security is full featured. Dave thrives on identifying threats and developing methods to solve complex problems. His specialties are intrusion detection/prevention, ethical hacking, forensics and analysis of malware and advanced threats. As a member of the IBM MSS Threat Research Team, Dave takes the intelligence he has gathered and turns out immediate tangible remedies that can be implemented within a customer’s network or on IBM MSS's own proprietary detection engines.Dave became interested in security back in the late 1980's and owned and operated a company that provided penetration and vulnerability testing service, one of the first of its kind. As the internet's footprint began to grow, it became clear to him there was a new problem on the horizon; protecting data. Dave worked with WheelGroup (later acquired by Cisco) where he helped develop NetRanger IDS and NetSonar. Dave also assisted with development of the very first IBM intrusion detection system, BillyGoat. Dave also has developed several other security based methods and systems which were patented for IBM.