Hack The Box - Chase Challenge: A Blue Team Forensics Walkthrough

The dim glow of the monitor was the only companion as server logs spat out an anomaly. One that shouldn't be there. In the digital shadows, systems whisper secrets, and sometimes, those whispers turn into a full-blown breach. Today, we're not patching a system; we're performing a digital autopsy. The target: Hack The Box's 'Chase' challenge, a low-difficulty but insightful dive into network forensics from a Blue Team perspective. Forget the flashy exploits for a moment; true mastery lies in understanding the aftermath, in piecing together the attacker's narrative from the digital breadcrumbs they leave behind.

This isn't about audacious intrusions; it's about meticulous observation. The 'Chase' challenge, rated a mere 2 out of 10 in difficulty, offers a perfect entry point for those looking to hone their incident response and forensic analysis skills. We'll dissect the network traffic, unravel the attacker's steps, and understand precisely how a system was compromised. For any serious security professional, understanding these fundamentals is not optional; it's the bedrock upon which robust defenses are built.

Introduction: The Echo of an Intrusion

The digital world is a tapestry of transactions, each packet a thread weaving through the network. When an attacker breaches a system, they don't just disappear; they leave echoes. As Blue Team analysts, our job is to listen to these echoes, to analyze the residual digital noise and reconstruct the events that transpired. The 'Chase' challenge on Hack The Box provides exactly this opportunity: a captured network traffic file (PCAP) that documents a compromise, waiting to be unraveled.

Understanding network forensics is paramount. It's the science of digital evidence collection and analysis. Without it, incident response is merely reactive guesswork. This walkthrough will guide you through the process of analyzing the 'Chase' PCAP, demonstrating how basic forensic techniques can reveal an attacker's actions.

Challenge Description: The Setup

The 'Chase' challenge positions itself as a forensic task. The objective is to analyze a provided PCAP file to find a hidden flag. The difficulty rating of 2/10 suggests that the techniques required are foundational, making it an ideal starting point for newcomers to network forensics. The narrative implies a successful intrusion where the attacker has likely established a foothold and potentially exfiltrated data or achieved their objective, leaving behind the clues we need.

In a real-world scenario, such a PCAP might be obtained from a network intrusion detection system (NIDS), a span port on a switch, or directly from a compromised host. The goal is to simulate the analysis phase of an incident response.

Initial File Triage: First Impressions

Upon receiving the PCAP file, the first step is always a preliminary examination. What kind of traffic is present? Are there any immediately obvious protocols or connections? For 'Chase', we'd typically place the file in our analysis environment and open it with Wireshark. This initial pass is about getting a feel for the data, looking for anomalies, large transfers, or unusual protocol usage. It's like a detective walking into a crime scene – observe everything before touching anything.

We're looking for things like:

  • Protocols in use (HTTP, DNS, SMB, etc.)
  • IP addresses involved
  • Connection patterns (one-to-one, many-to-one, etc.)
  • Any encrypted traffic that might hide malicious activity.

Wireshark: The Global Overview

Wireshark is the undisputed king of packet analysis. For the 'Chase' challenge, it's our primary tool. The initial overview involves looking at the statistics available within Wireshark:

  • Statistics -> Protocol Hierarchy: Gives a breakdown of all protocols used in the capture. This helps identify if unexpected protocols are present.
  • Statistics -> Conversations: Lists all communication endpoints (IP addresses, TCP/UDP ports) and the amount of data exchanged. This is crucial for identifying the main actors and communication flows.
  • Statistics -> Endpoints: Similar to Conversations but provides a list of all endpoints and their MAC addresses.

From here, we can start to identify the source and destination IP addresses that are communicating. A low-difficulty challenge like 'Chase' will likely have a clear path from an external attacker IP to an internal victim IP.

Mapping the Attack: Visualizing the Narrative

Once the key IP addresses and protocols are identified, the next logical step is to visualize the attack's path. This involves reconstructing the attacker's actions chronologically. In Wireshark, this can be achieved by:

  • Filtering traffic: Applying display filters to isolate specific conversations (e.g., `ip.addr == ATTACKER_IP && ip.addr == VICTIM_IP`).
  • Following TCP/UDP Streams: Right-clicking on a packet belonging to a suspicious conversation and selecting 'Follow > TCP Stream' (or UDP Stream) allows you to see the reassembled data exchanged between the two endpoints. This is where the payload and commands often become visible.

By following streams, we can start to piece together the sequence of events: the initial connection, any exploitation attempts, command execution, and potential data exfiltration or flag retrieval.

Deep Dive: Following the Threads

The 'Chase' challenge likely involves a web-based compromise. Therefore, significant focus will be placed on HTTP/HTTPS traffic. Following the TCP streams for HTTP connections is critical. This is where we might see requests and responses containing:

  • Malicious links or file downloads.
  • Webshell payloads (e.g., PHP, ASP, JSP webshells).
  • Commands being sent to a compromised server.
  • Output of commands executed on the victim machine.

An attacker might use a webshell to gain a reverse shell. Analyzing these streams helps confirm the method of entry and the initial actions taken by the intruder.

Webshell Forensics: The Attacker's Foothold

Webshells are a common tool for attackers to gain command execution on a web server. In the 'Chase' PCAP, we might observe HTTP POST requests with suspicious parameters or data that, when interpreted by the web server, execute commands. Identifying the specific webshell (e.g., Visual Basic VB webshell, as indicated by the original content) is key.

Analyzing the content of these requests can reveal:

  • The type of webshell being used.
  • The commands being passed to the shell.
  • The parameters used to interact with the shell.

Understanding the webshell's functionality helps us infer what the attacker intended to achieve and what commands they likely ran subsequently.

Reverse Shell Commands: What Was Executed?

Once a webshell is exploited, an attacker often attempts to establish a reverse shell. This allows for more interactive command execution. In the PCAP, this would typically manifest as a TCP connection from the victim server back to the attacker's machine, often on a non-standard port. Following this stream is paramount.

Here, we'd look for:

  • Standard reconnaissance commands like `whoami`, `hostname`, `ipconfig`/`ifconfig`, `pwd`, `ls`/`dir`.
  • Commands used to download further tools or scripts.
  • Commands to elevate privileges.
  • Crucially, any commands related to finding or exfiltrating the flag.

The provided timestamps suggest a focus on identifying these executed commands. A common technique is to look for shell history files or command output within the captured traffic.

The Final Prize: Extracting the Flag

The ultimate goal in these challenges is to find the flag. In 'Chase', the hint mentions "Getting flag from base32 on odd filename." This suggests the flag might be encoded (Base32) and stored in a file with an unusual name. The commands executed in the reverse shell would lead us to discover this file.

The process would involve:

  1. Identifying the command that created or accessed the file containing the flag.
  2. Noting the filename, especially if it's peculiar.
  3. Capturing the flag's content from the traffic or directly from the executed command output.
  4. Decoding the flag if necessary (in this case, from Base32).

This final step ties together all the previous forensic analysis, confirming the attacker's objective and successfully retrieving the prize.

Engineer's Verdict: Value of Blue Team Fundamentals

The 'Chase' challenge, despite its low difficulty, is invaluable. It reinforces the core principles of network forensics and incident response. For any organization, investing in Blue Team capabilities is non-negotiable. Understanding how to analyze PCAPs, identify malicious traffic, and reconstruct attacker actions allows for faster detection, more effective containment, and thorough remediation.

Pros:

  • Excellent introduction to network forensics.
  • Reinforces critical Wireshark skills.
  • Highlights common attack vectors (webshells, reverse shells).
  • Provides practical experience in flag retrieval.

Cons:

  • Lacks the complexity of real-world advanced persistent threats (APTs).
  • May oversimplify certain forensic processes for brevity.

Verdict: Essential for foundational Blue Team training. It's a stepping stone, not the destination. Don't let the low difficulty fool you into dismissing its importance.

Operator's Arsenal: Essential Forensics Tools

To effectively tackle challenges like 'Chase' and real-world incidents, a well-equipped arsenal is crucial. While Wireshark is dominant for packet analysis, other tools complement the Blue Team's efforts:

  • Wireshark: The cornerstone for deep packet inspection. Mastering its filters and features is essential. Consider the professional versions or supplementary plugins for advanced analysis.
  • NetworkMiner: Excellent for extracting artifacts (files, images, credentials) directly from PCAP files without manual stream following.
  • KAPE (Kolibri's Advanced Forensics Format Enhancer): A powerful triage and artifact collection tool for live systems, invaluable in rapid incident response.
  • Volatility Framework: For memory forensics. While not directly used in 'Chase', understanding memory analysis is vital for detecting sophisticated threats.
  • Sysmon: A Windows system service and device driver that monitors and logs system activity – crucial for collecting detailed forensic data.
  • SIEM Solutions (e.g., Splunk, ELK Stack): For aggregating and analyzing logs from multiple sources in real-time.
  • Books: "The Practice of Network Security Monitoring" by Richard Bejtlich, "Network Forensics: Tracking Hackers Through Cyberspace" by Nelson, Phillips, and Enfinger.
  • Certifications: GIAC Certified Forensic Analyst (GCFA), Certified Incident Handler (GCIH).

Practical Workshop: Analyzing PCAP with Wireshark

Let's simulate the core steps for analyzing the 'Chase' PCAP using Wireshark. Assume you have downloaded the PCAP file.

  1. Launch Wireshark: Open Wireshark and load the 'Chase' PCAP file.
  2. Initial Statistics: Navigate to Statistics > Conversations.
    • Identify the IP addresses involved. Look for a potential attacker IP communicating with a victim server IP. Note the protocols and data volumes.
  3. Filter for Key Protocols: Apply a display filter like http or tcp.port == 80 (if HTTP is suspected) to narrow down the traffic.
  4. Identify Suspicious HTTP Requests: Look for POST requests, requests with unusual query parameters, or responses indicating file uploads/downloads.
  5. Follow TCP Streams: Right-click on a suspicious HTTP request packet and select Follow > TCP Stream.
    • Examine the request and response data. Search for patterns resembling webshell code or commands being sent.
    • If a reverse shell is established, you'll likely see traffic on a different port. Filter for that specific port (e.g., tcp.port == 12345 if the attacker used port 12345).
  6. Analyze Reverse Shell Traffic: Follow the TCP stream for the reverse shell connection.
    • Look for command outputs. Commands like ls, dir, whoami, pwd are common.
    • Identify any commands used to locate or display the flag.
  7. Decode the Flag: If the flag is encoded (e.g., Base32), use an online decoder or a tool like Python to decode it. Example command execution might have printed the flag in Base32, requiring a command like: 
    echo "FLAG_IN_BASE32" | base32 -d

This structured approach ensures that no critical piece of evidence is missed.

Frequently Asked Questions

Q1: What is the primary goal of a Blue Team in cybersecurity?
A1: The Blue Team's primary role is to defend an organization's information systems against cyber threats. This includes monitoring, detection, incident response, and proactive defense strategies.

Q2: Why is Wireshark essential for Blue Team analysts?
A2: Wireshark provides deep visibility into network traffic. It allows analysts to capture, inspect, and analyze network packets in detail, which is critical for understanding communication patterns, detecting anomalies, and investigating security incidents.

Q3: What is a PCAP file?
A3: A PCAP (Packet Capture) file is a file that contains network packet data. It's essentially a recording of network traffic that can be replayed and analyzed later using tools like Wireshark.

Q4: How does network forensics differ from host forensics?
A4: Network forensics focuses on analyzing network traffic data (packets, logs) to understand events as they occur across a network. Host forensics, on the other hand, focuses on analyzing data stored on individual computer systems (disk images, memory dumps, logs).

The Contract: Your Next Forensic Hunt

You've dissected the 'Chase' challenge, understood the attacker's path, and retrieved the flag. Now, the real work begins. The digital ether is vast and filled with ghosts of intrusions past. Your contract is this: find another low-difficulty forensic challenge online (from platforms like TryHackMe, Hack The Box, or others) and perform a similar analysis. Document your findings, focusing on how you identified the attacker's initial vector and their subsequent actions. The true test isn't solving one puzzle, but building the methodology to solve them all.

Now, it's your turn. Have you encountered challenges where an unusual filename held the key? What other techniques do you rely on for initial PCAP triage beyond what's covered here? Share your insights and your preferred tools in the comments below. Let's build a collective knowledge base, one packet at a time.

Source: HackTheBox CTF - Chase Challenge

Category: Forensic

Difficulty: 2/10

For further exploration, check out the full walkthrough video: [YouTube Link Placeholder]

Connect with the community: [Discord Link Placeholder], [Twitter Link Placeholder]

at
Labels: , , , , , ,

No comments:

Post a Comment

Subscribe to: Post Comments (Atom)