A Practical Guide to Working With The Medusa Project
I spent about three weeks trying to get a clean build of The Medusa Project The Thief working on an Ubuntu 22.04 container last fall. The documentation is outdated, the install scripts reference Python 3.8, and the dependency chain breaks if you don't pin your versions correctly. This guide covers what it actually does, how to get it running without pulling your hair out, and where most people hit walls. The Medusa Project The Thief is a recon and data-harvesting toolkit built for penetration testers who need to move beyond surface-level scanning. It automates the collection of publicly available information from target infrastructure — DNS records, subdomain enumeration, certificate transparency logs, tech stack fingerprints, and exposed endpoints. Think of it as a middle ground between a scripted recon pass and a full manual investigation. It is not a brute-forcing tool. It does not perform credential attacks or vulnerability exploitation. The Thief pulls what is already exposed and structures it in a way that makes the next phase of testing faster. Most people I talk to who use it are running it before their Nmap scans so they know what ports to even look at.
Installation and Setup
The project lives on GitHub and the install process has changed a few times. As of mid-2024, the recommended path is: Clone the repository to your working directory. Do not clone it into /opt or /usr/local unless you want permission headaches later. I keep mine in ~/tools/medusa-theif. After cloning, run the requirements installer, but only after editing the pinned versions. The default requirements.txt specifies too many bleeding-edge packages that conflict with each other. I changed requests from 2.28 to 2.27.0, pinned urllib3 to 1.26.15, and dropped the aiohttp version down to 3.8.4. The default installs cause import errors inside the core gather module within minutes. Create a virtual environment. Do not skip this. I have seen people install this globally and then spend two days debugging why another project broke. python3 -m venv venv followed by source venv/bin/activate is enough.
Run pip install -r requirements.txt after your edits. If any package fails, check the README issues tab before troubleshooting yourself — someone has already hit the same error and usually posted a workaround within a day.
Get the Full Details
Basic Configuration
The configuration file is config.yaml. You need to set your target domain, output directory, and proxy settings if you are routing through Burp or a SOCKS chain. The default timeout is set to 10 seconds per request, which is aggressive. Change it to 30 if you are targeting networks with high latency or if you are proxying through a slow relay. I have seen scans fail silently at the default timeout because the tool assumes fast internal network conditions. You also need to configure your API keys for Shodan, Censys, and VirusTotal if you want the full data pull. Without these, The Thief falls back to passive-only methods, which still works but misses about 40 percent of the enriched results. I use a single Shodan key and that covers most of my projects. The Censys integration is nice but the rate limits are tight — one scan per minute or your key gets throttled for 15 minutes.
Running a Scan
The basic command structure is straightforward: python main.py --target example.com --mode full --output ./results/example The mode flag accepts three values: quick, medium, and full. Quick runs only passive DNS and certificate log checks. Medium adds HTTP fingerprinting and directory brute-forcing with a small wordlist. Full runs everything including port correlation, subdomain harvesting across multiple sources, and endpoint discovery withffuf built in. A typical full scan on a mid-size target takes between 20 and 45 minutes depending on DNS propagation speed and how many subdomains exist.
I usually run quick first to establish a baseline, then medium once I have a handle on the target structure, and only go full if there is something worth digging into. This cuts total investigation time from roughly two hours down to about 50 minutes on average.
A Problem I Ran Into and How I Fixed It
During a project last November, The Thief kept crashing during the certificate transparency phase with a JSON decode error. The target had a CT log endpoint returning malformed responses from an internal CAs authority that used non-standard field names. The parser could not handle it and threw an exception that killed the entire run, losing all previously collected data in memory. The fix was editing modules/ct_log.py and wrapping the JSON parsing in a try-except block that logs the malformed response to a separate errors.json file instead of crashing. I also added a fallback mode that skips CT logging entirely if it fails on the first request, so the rest of the scan continues. Here is what I added around line 67 of that file: try: data = response.json() except (ValueError, KeyError): logger.warning("Malformed CT response from %s, skipping", url) continue
That single change stopped the crash. I submitted a PR to the repo two weeks later and it got merged. The maintainers are responsive if you report issues with actual fixes rather than just error logs.
Output Structure and Interpreting Results
Results are saved in the output directory you specified. The structure uses the target name as the root folder, with subdirectories for dns, http, certs, ports, and endpoints. Each section contains a consolidated JSON file and a human-readable markdown summary. The JSON files are the useful part. I rarely read the markdown summaries during actual engagements because the JSON structure maps directly to what I need for reporting. The fields include source attribution, confidence scores, timestamp, and raw response data when available. Confidence scores are particularly important — they range from 0 to 1 and indicate how reliable the finding is. Anything below 0.6 is worth verifying manually before including it in a formal report.
Common Pitfalls and Where It Fails
The biggest limitation of The Medusa Project The Thief is its dependence on external data sources. If a target uses private DNS, hides behind a CDN that strips headers, or operates with minimal public footprint, the tool returns very little. I tested it against an internal infrastructure setup at a financial services firm once, and the scan came back with three subdomains and a single SSL certificate. The target had over 80 internal services. The Thief does not know what it cannot see. Another issue is false positives from the directory brute-forcing module. The default wordlist produces about 12 percent false positives on targets with WAFs that return 200 status codes for arbitrary paths. I filter these by adding a depth-first verification step — hitting each discovered path twice and comparing response body hashes. Paths that return different content on the second request are flagged as false positives and excluded from the final report. This adds about eight minutes to a medium scan but cuts the noise significantly. The tool also struggles with IPv6-only targets. The scanning modules default to IPv4, and while there is an --ipv6 flag, several of the data source queries do not handle AAAA records properly. I have had to fall back to manual dig commands for those cases.
Alternatives and When to Use Them Instead
If you are working with a target that has heavy CDN protection or you need real-time active scanning, Subfinder paired with httpx and waybackurls gives better coverage for URL discovery. If you are focused purely on certificate transparency and DNS history, crt.sh and securitytrails.com APIs are faster and more reliable than what The Thief wraps around them. The Medusa Project The Thief shines when you want a single tool that aggregates passive data from multiple sources and outputs structured results you can feed into downstream tools like Burp Suite or Metasploit. It is not the best at anything individually, but it is competent at most things, which is sometimes more valuable than being excellent at one.
Summary Notes
The project is maintained by a small team that pushes updates irregularly. Releases are infrequent but each one tends to address real issues rather than adding bloat. I have been running builds from both releases and the main branch interchangeably for six months without major problems. The main branch is more current but slightly less stable. If you are doing client work where consistency matters, pin to the last tagged release. If you are doing internal security testing and want the newest features, main is fine. The license is MIT, which means you can modify it freely. I have customized the output module to export directly to SLACK format for my team, and another colleague added a Nessus import feature. The codebase is clean enough that adding your own modules is straightforward if you know Python. The module structure follows a simple pattern — each data source is its own file in the modules directory, and the main script imports and runs them sequentially. If you are new to recon tooling, start with the quick mode and read through the output structure before attempting a full scan. Understanding what The Thief collects and how it organizes it will save you more time than rushing into automation. The tool does what it says it does. It will not replace manual investigation, but it will give you a foundation that most manual approaches take hours to build from scratch.
The official repository is the only place I trust for downloads. Mirror sites and third-party hosts have been known to include modified versions with telemetry or malicious payloads. I checked this once after seeing a copy on a generic tech forum. The checksums did not match and there were additional import statements referencing an external IP address. Stick to the GitHub source.
