Server-side Attacks

Server-side Attacks  Medium

A backend that handles user-supplied input insecurely can lead to sensitive information disclosure and remote code execution. This module covers how to identify and exploit server-side bugs. This module introduces Server-Side Request Forgery (SSRF), Server-Side Template Injection (SSTI), and Server-Side Includes (SSI) injection attacks, alongside other server-side vulnerabilities.

Created by Andres D

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When interacting with modern web applications, we need to be aware that multiple machines and components are likely involved in the process. There may be intrusion detection/prevention systems, content delivery networks for better performance, load balancers, reverse proxies, other application servers, template engines, and database servers between us and the application server. As you can imagine, the IP associated with the domain name may have nothing to do with the actual application server. When we issue HTTP requests to a target application, all the machines and components involved in the process do not simply pass requests through but also interpret them in order, for example, to apply restrictions or identify and block attacks.

At this point, we need to consider the below:

  • Do those intermediary machines and components interpret and treat the requests the same way the final application server does? If not, this could be the root cause of a security issue.
  • Do those intermediary machines and components perform (enough) validation before the user request hits the final application server? If not, this could also be the root cause of a security issue.

The attack scenarios mentioned above leverage the trust between the final application server and the intermediary machines and components. However, there are scenarios where server-side attacks can be executed against the hosting server itself without the interference of any intermediary machines and components, leveraging the trust between the server and itself. In the latter scenarios, a URL is usually passed with a hostname of or localhost.

From a penetration tester's perspective, it is worth checking for inefficiencies in how user requests are being treated or validated from these types of intermediary machines and components or the application server itself since they can lead to severe information leakage or even remote code execution.

This module will discuss the basics of identifying and exploiting server-side bugs.

This module is broken into sections with accompanying hands-on exercises to practice each of the tactics and techniques we cover. The module ends with a practical hands-on skills assessment to gauge your understanding of the various topic areas.

You can start and stop the module at any time and pick up where you left off. There is no time limit or "grading," but you must complete all of the exercises and the skills assessment to receive the maximum number of cubes and have this module marked as complete in any paths you have chosen.

As you work through the module, you will see example commands and command output for the various topics introduced. It is worth reproducing as many of these examples as possible to reinforce further the concepts presented in each section. You can do this in the PwnBox provided in the interactive sections or your virtual machine.

The module is classified as "Medium" and assumes a working knowledge of the Linux command line and an understanding of information security fundamentals. The module also assumes basic knowledge of web applications and web requests. It will build on this understanding to teach how server-side bugs can be exploited.

In addition to the above, a firm grasp of the following modules can be considered as prerequisites for the successful completion of this module:

  • Linux Fundamentals
  • Web Requests
  • Introduction to Web Applications
  • Using Web Proxies
  • Cross-Site Scripting (XSS)


  • Introduction to Server-Side Attacks
  • AJP Proxy
  • Nginx Reverse Proxy & AJP
  • Apache Reverse Proxy & AJP
  • Server-Side Request Forgery (SSRF) Overview
  • SSRF Exploitation Example
  • Blind SSRF
  • Blind SSRF Exploitation Example
  • Time-Based SSRF
  • Server-Side Includes Overview
  • SSI Injection Exploitation Example
  • Edge-Side Includes (ESI)
  • Introduction to Template Engines
  • SSTI Identification
  • SSTI Exploitation Example 1
  • SSTI Exploitation Example 2
  • SSTI Exploitation Example 3
  • Attacking XSLT
  • Server-Side Attacks - Skills Assessment

Relevant Paths

This module progresses you towards the following Paths

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Bug Bounty Hunter

Medium 257 Sections

Cubes Required: 1410

The Bug Bounty Hunter Job Role Path is for individuals who want to enter the world of Bug Bounty Hunting with little to no prior experience. This path covers core web application security assessment and bug bounty hunting concepts and provides a deep understanding of the attack tactics used during bug bounty hunting. Armed with the necessary theoretical background, multiple practical exercises, and a proven bug bounty hunting methodology, students will go through all bug bounty hunting stages, from reconnaissance and bug identification to exploitation, documentation, and communication to vendors/programs. Upon completing this job role path, you will have become proficient in the most common bug bounty hunting and attack techniques against web applications and be in the position of professionally reporting bugs to a vendor.

  Web Requests

Fundamental 8 Sections

This module introduces the topic of HTTP web requests and how different web applications utilize them to communicate with their backends.

  Introduction to Web Applications

Fundamental 17 Sections

In the Introduction to Web Applications module, you will learn all of the basics of how web applications work and begin to look at them from an information security perspective.

  Using Web Proxies

Easy 15 Sections

Web application penetration testing frameworks are an essential part of any web penetration test. This module will teach you two of the best frameworks: Burp Suite and OWASP ZAP.

  Information Gathering - Web Edition

Easy 10 Sections

This module covers techniques for identifying and analyzing an organization's web application-based attack surface and tech stack. Information gathering is an essential part of any web application penetration test, and it can be performed either passively or actively.

  Attacking Web Applications with Ffuf

Easy 13 Sections

This module covers the fundamental enumeration skills of web fuzzing and directory brute forcing using the Ffuf tool. The techniques learned in this module will help us in locating hidden pages, directories, and parameters when targeting web applications.

  JavaScript Deobfuscation

Easy 11 Sections

This module will take you step-by-step through the fundamentals of JavaScript Deobfuscation until you can deobfuscate basic JavaScript code and understand its purpose.

  Cross-Site Scripting (XSS)

Easy 10 Sections

Cross-Site Scripting (XSS) vulnerabilities are among the most common web application vulnerabilities. An XSS vulnerability may allow an attacker to execute arbitrary JavaScript code within the target's browser and result in complete web application compromise if chained together with other vulnerabilities. This module will teach you how to identify XSS vulnerabilities and exploit them.

  SQL Injection Fundamentals

Medium 17 Sections

Databases are an important part of web application infrastructure and SQL (Structured Query Language) to store, retrieve, and manipulate information stored in them. SQL injection is a code injection technique used to take advantage of coding vulnerabilities and inject SQL queries via an application to bypass authentication, retrieve data from the back-end database, or achieve code execution on the underlying server.

  SQLMap Essentials

Easy 11 Sections

The SQLMap Essentials module will teach you the basics of using SQLMap to discover various types of SQL Injection vulnerabilities, all the way to the advanced enumeration of databases to retrieve all data of interest.

  Command Injections

Medium 12 Sections

Command injection vulnerabilities can be leveraged to compromise a hosting server and its entire network. This module will teach you how to identify and exploit command injection vulnerabilities and how to use various filter bypassing techniques to avoid security mitigations.

  File Upload Attacks

Medium 11 Sections

Arbitrary file uploads are among the most critical web vulnerabilities. These flaws enable attackers to upload malicious files, execute arbitrary commands on the back-end server, and even take control over the entire server and all web applications hosted on it and potentially gain access to sensitive data or cause a service disruption.

  Server-side Attacks

Medium 19 Sections

A backend that handles user-supplied input insecurely can lead to sensitive information disclosure and remote code execution. This module covers how to identify and exploit server-side bugs. This module introduces Server-Side Request Forgery (SSRF), Server-Side Template Injection (SSTI), and Server-Side Includes (SSI) injection attacks, alongside other server-side vulnerabilities.

  Login Brute Forcing

Easy 11 Sections

Learn how to brute force logins for various types of services and create custom wordlists based on your target.

  Broken Authentication

Medium 14 Sections

Authentication is probably the most straightforward and prevalent measure used to secure access to resources, and it's the first line of defense against unauthorized access. Broken authentication is currently listed as #7 on the 2021 OWASP Top 10 Web Application Security Risks, falling under the broader category of Identification and Authentication failures. A vulnerability or misconfiguration at the authentication stage can devastatingly impact an application's overall security.

  Web Attacks

Medium 18 Sections

This module covers three common web vulnerabilities, HTTP Verb Tampering, IDOR, and XXE, each of which can have a significant impact on a company's systems. We will cover how to identify, exploit, and prevent each of them through various methods.

  File Inclusion

Medium 11 Sections

File Inclusion is a common web application vulnerability, which can be easily overlooked as part of a web application's functionality.

  Session Security

Medium 14 Sections

Maintaining and keeping track of a user's session is an integral part of web applications. It is an area that requires extensive testing to ensure it is set up robustly and securely. This module covers the most common attacks and vulnerabilities that can affect web application sessions, such as Session Hijacking, Session Fixation, Cross-Site Request Forgery, Cross-Site Scripting, and Open Redirects.

  Web Service & API Attacks

Medium 13 Sections

Web services and APIs are frequently exposed to provide certain functionalities in a programmatic way between heterogeneous devices and software components. Both web services and APIs can assist in integrating different applications or facilitate separation within a given application. This module covers how to identify the functionality a web service or API offers and exploit any security-related inefficiencies.

  Hacking WordPress

Easy 16 Sections

WordPress is an open-source Content Management System (CMS) that can be used for multiple purposes.

  Bug Bounty Hunting Process

Easy 6 Sections

Bug bounty programs encourage security researchers to identify bugs and submit vulnerability reports. Getting into the world of bug bounty hunting without any prior experience can be a daunting task, though. This module covers the bug bounty hunting process to help you start bug bounty hunting in an organized and well-structured way. It's all about effectiveness and professionally communicating your findings.

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