Everything You Need To Know About Web Shells


So let’s talk about Web Shells, something many of us are already familiar with, but to level the field – what is a web shell?

A web shell is a script that can be uploaded to a web server to enable remote administration of the machine. Infected web servers can be either Internet-facing or internal to the network, where the web shell is used to pivot further to internal hosts.

Everything You Need To Know About Web Shells

We have written about various web shell implementations and tools such as:

Weevely 3 – Weaponized PHP Web Shell
A Collection of Web Backdoors & Shells – cmdasp cmdjsp jsp-reverse php-backdoor
InsomniaShell – ASP.NET Reverse Shell Or Bind Shell

And various other mentions here and there.

Now, Acunetix has come out with a great, really comprehensive 5 part article about web shells which covers:

Which covers pretty much everything apart from the really advanced stuff, an introduction and then obviously PHP as it’s still the most widespread language for commonly installed CMS packages (WordPress, Joomla, Drupal etc), then hiding your web shells, what you can do with web shells and finishing with detecting and preventing the installation of web shells.

A web-shell is a malicious script used by an attacker with the intent to escalate and maintain persistent access on an already compromised web application. A web-shell itself cannot attack or exploit a remote vulnerability, so it is always the second step of an attack (this stage is also referred to as post-exploitation).

An attacker can take advantage of common vulnerabilities such as SQL injection, remote file inclusion (RFI), FTP, or even use cross-site scripting (XSS) as part of a social engineering attack in order to upload the malicious script. The common functionality includes but is not limited to shell command execution, code execution, database enumeration and file management.

From – Part 1

And the series to conclude:

As we have seen, coding and using a web-shell is not difficult. Unfortunately, many web servers are setup in such a way where even a simple script is enough to cause significant damage. This is the main reason as to why there are thousands of publicly available web-shells. The fact that so many variations exist, make it difficult for intrusion detection and intrusion prevention systems (IDS/IPS) to detect them; especially if they are using signatures to detect such web shells. Some web-shells are very sophisticated and they are almost impossible to be detected, even with behavioral analysis.

Having said this, early on in this article series, we had established that web-shells are post-exploitation tools. This means that the best way to prevent exploitation, is to prevent them from being uploaded in the first place.

From – Part 5

My best tip, if you’re a WordPress user to prevent the usage of PHP based exploits and/or web shell is to add this to your nginx config file:

So yah, read all 5 parts and you’ll have to been to Web Shell starter school.

Then go and explore this repo to find all kinds of web shells in different languages – https://github.com/tennc/webshell

Enjoy!

Posted in: Web Hacking

, ,


Latest Posts:


zBang - Privileged Account Threat Detection Tool zBang – Privileged Account Threat Detection Tool
zBang is a risk assessment tool for Privileged Account Threat Detection on a scanned network, organizations & red teams can use it to identify attack vectors
Memhunter - Automated Memory Resident Malware Detection Memhunter – Automated Memory Resident Malware Detection
Memhunter is an Automated Memory Resident Malware Detection tool for the hunting of memory resident malware at scale, improving threat hunter analysis process.
Sandcastle - AWS S3 Bucket Enumeration Tool Sandcastle – AWS S3 Bucket Enumeration Tool
Sandcastle is an Amazon AWS S3 Bucket Enumeration Tool, formerly known as bucketCrawler. The script takes a target's name as the stem argument (e.g. shopify).
Astra - API Automated Security Testing For REST Astra – API Automated Security Testing For REST
Astra is a Python-based tool for API Automated Security Testing, REST API penetration testing is complex due to continuous changes in existing APIs.
Judas DNS - Nameserver DNS Poisoning Attack Tool Judas DNS – Nameserver DNS Poisoning Attack Tool
Judas DNS is a Nameserver DNS Poisoning Attack Tool which functions as a DNS proxy server built to be deployed in place of a taken over nameserver to perform targeted exploitation.
dsniff Download - Tools for Network Auditing & Password Sniffing dsniff Download – Tools for Network Auditing & Password Sniffing
Dsniff download is a collection of tools for network auditing & penetration testing. Dsniff, filesnarf, mailsnarf, msgsnarf, URLsnarf, and WebSpy passively monitor a network


Comments are closed.