The Hidden Smile - Forensic Analysis of the Compromised Mona Lisa

When an attacker infiltrates a system, they rarely settle for just stealing information and disappearing. They leave hidden clues in seemingly innocent places and set up mechanisms to return whenever they wish. In this lab, you will step into the shoes of a digital forensic analyst facing a live incident, with the mission of deciphering the secrets hidden within the Mona Lisa.

⚠️ Warning: You are dealing with an actively compromised system Unlike post-mortem forensic analysis (system powered off), here the attacker may still be present and their malicious mechanisms are still running. This means every action you take may be observed, and any mistake could alert the intruder or corrupt critical evidence.

Live Incident Methodology: ORDER OF VOLATILITY

In an actively compromised system, the order of evidence collection is critical. The most volatile data disappears first:

• CPU registers and RAM memory (lost on reboot)
• Active network connections (constantly changing)
• Running processes (can terminate at any moment)
• Temporary files (overwritten or deleted)
• Persistent files (less volatile, but can be modified)

Before diving into the system investigation, think like a true analyst: Does this image of the Mona Lisa contain only pixels of Renaissance art? What tools would you use to extract every byte of available information without alerting the attacker?

Golden rule: In live incident forensics, every command you run may be monitored. Act with stealth and precision. The key is to assume nothing. In digital forensics, even the world's most famous artwork can be an attack vector.

Hypothesis: the system as a crime scene

The initial symptoms point to something deeper than just a compromised image. In Linux, experienced attackers often establish persistence through:

• Malicious daemon processes running continuously in the background.
• Scheduled tasks (cron jobs) configured to maintain their presence.
• Constant modification of files containing critical information.

Forensic investigation: live incident protocol

An analyst must follow a protocol for active incidents. Look for inconsistencies, suspicious coordinates, or information that shouldn't be there.

1. Initial documentation: Before touching anything, document the current state of the system. A poorly executed command can erase evidence forever.

2. List active processes:

1ps aux --sort=start_time | less

Examine recent processes you don't recognize, especially those with names related to art, images, or seemingly random strings.

1. Search for scheduled tasks:

1crontab -l
2ls -l /etc/cron.*
3sudo grep -R "" /var/spool/cron/crontabs

The key is to distinguish legitimate system tasks from those that seem out of place.

1. Discreet monitoring: Observe changes without generating much activity

1watch -n 5 'ps aux | tail -10'  # Most recent processes
2watch -n 10 cat /path/to/suspicious/file

Critical warning: In a live incident, the attacker can:

• Detect your investigation commands
• Modify evidence in real time
• Trigger self-destruct mechanisms
• Delete logs of their activity

The key is to be invisible while collecting evidence.

Comprehensive neutralization

When you locate both the source of the hidden information and the system's persistence, your job as an analyst will be to:

• Stop the malicious process maintaining activity.
• Disable the scheduled task that reactivates it.
• Remove or isolate the artifact that allows the attacker to maintain access.
• Pivot to the intruder's account.

Remember: the investigation must be thorough. If you only neutralize part of the attack but don't access all the information, the case will remain incomplete.

Forensic investigator mindset

This challenge is not just a simple "find the hidden flag." It's an exercise to train the mindset of a professional analyst:

• Analyze digital evidence without contaminating it.
• Correlate clues from multiple sources.
• Follow digital trails throughout the system.
• Neutralize threats systematically.
• Document findings for future cases.

Don't think in terms of "which tool gives me the answer," but rather how a professional forensic analyst connects scattered digital evidence, neutralizes active threats, and reconstructs the full story of an incident. That is the skill this lab aims to develop.