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CTF OSINT

Free

Master open source intelligence for CTF challenges.

by ljagiello3k stars on ljagiello/ctf-skills
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Updated Jul 31, 2026
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Free · Opens the source repo

What CTF OSINT does

CTF OSINT is a skill designed for participants in Capture The Flag (CTF) competitions who need to gather open source intelligence (OSINT) from various public sources. This skill provides a quick reference for various OSINT techniques, allowing users to efficiently collect information from social media, geolocation data, DNS records, and more. Each technique is summarized in a concise manner, with supporting files available for deeper exploration of the methods involved.

The skill includes a range of techniques such as username enumeration, reverse image search, and Google dorking, making it a versatile tool for information gathering. Users can leverage resources like the Wayback Machine and Tor relays to uncover historical data and anonymized sources. Additionally, the skill offers methods for identifying unknown data, such as hashes and coordinates, which can be crucial in solving CTF challenges.

For those looking to enhance their OSINT capabilities, CTF OSINT provides a structured approach to leveraging various tools and techniques. The bundled files cover specific areas like social media analysis, geolocation techniques, and web and DNS reconnaissance, offering detailed guidance on how to implement each method effectively. This skill is particularly useful for security researchers, ethical hackers, and anyone involved in competitive CTF events who needs to gather and analyze publicly available information.

In summary, CTF OSINT is an essential resource for anyone involved in CTF challenges, providing a comprehensive toolkit for effective OSINT gathering. By utilizing the techniques outlined in this skill, users can streamline their information collection process and improve their chances of success in CTF competitions.

When to use it

Use this skill when participating in CTF competitions that require OSINT techniques to gather data from public sources.

When not to use it

This skill may not be suitable for tasks that involve live exploitation or forensic analysis, where other specialized tools are more appropriate.

What you can build with it

Social Media Analysis

Use the techniques in social-media.md to extract user data and historical information from platforms like Twitter and Tumblr.

Geolocation Techniques

Apply methods from geolocation-and-media.md to analyze images and determine their geographic origin using metadata and visual clues.

DNS Reconnaissance

Utilize web-and-dns.md to perform DNS queries and gather information about domains, including WHOIS data and historical records.

How to install CTF OSINT

View source

1. Install with the skills CLI

npx skills add ljagiello/ctf-skills/ctf-osint --agent claude-code

2. Or install it manually

Download the skill folder and drop it into ~/.claude/skills/ for all projects, or .claude/skills/ to scope it to one repo. Restart Claude Code so it picks up the new skill.

Anthropic's agentic coding CLI, and the reference implementation of Agent Skills. Drop a skill folder into ~/.claude/skills and Claude Code loads it automatically whenever a task matches the skill's description. Claude Code docs

Inside SKILL.md

Written by ljagiello

CTF OSINT

Quick reference for OSINT CTF challenges. Each technique has a one-liner here; see supporting files for full details.

Prerequisites

Python packages (all platforms):

pip install shodan Pillow

Linux (apt):

apt install whois dnsutils nmap libimage-exiftool-perl imagemagick curl

macOS (Homebrew):

brew install whois bind nmap exiftool imagemagick curl

Additional Resources

  • social-media.md - Twitter/X (user IDs, Snowflake timestamps, Nitter, memory.lol, Wayback CDX), Tumblr (blog checks, post JSON, avatars), BlueSky search + API, Unicode homoglyph steganography, Discord API, username OSINT (namechk, whatsmyname, Osint Industries), username metadata mining (postal codes), platform false positives, multi-platform chains, Strava fitness route OSINT
  • geolocation-and-media.md - Image analysis, reverse image search (including Baidu for China), Google Lens cropped region search, reflected/mirrored text reading, geolocation techniques (railroad signs, infrastructure maps, MGRS), Google Plus Codes, EXIF/metadata, hardware identification, newspaper archives, IP geolocation, Google Street View panorama matching, What3Words micro-landmark matching, Google Maps crowd-sourced photo verification, Overpass Turbo spatial queries, music-themed landmark geolocation with key encoding
  • web-and-dns.md - Google dorking (including TBS image filters), Google Docs/Sheets enumeration, DNS recon (TXT, zone transfers), Wayback Machine, FEC research, Tor relay lookups, GitHub repository analysis, Telegram bot investigation, WHOIS investigation (reverse WHOIS, historical WHOIS, IP/ASN lookup), fake service banner detection via nmap fingerprinting

When to Pivot

  • If you already have the files or packets locally and now need extraction or carving, switch to /ctf-forensics.
  • If the task becomes active exploitation of a live HTTP service, switch to /ctf-web.
  • If you uncover malware samples, beacons, or suspicious binaries during attribution, switch to /ctf-malware.

Quick Start Commands

# DNS recon
dig -t any target.com
dig -t txt target.com
dig axfr @ns.target.com target.com
whois target.com

# Image metadata
exiftool image.jpg
identify -verbose image.jpg | head -30

# Web archive
curl "https://web.archive.org/web/20230101*/target.com"

# Username lookup
curl -s "https://whatsmyname.app/api/lookup?username=<user>"

# Shodan
shodan search "hostname:target.com"
shodan host <ip>

String Identification

  • 40 hex chars -> SHA-1 (Tor fingerprint)
  • 64 hex chars -> SHA-256
  • 32 hex chars -> MD5

Twitter/X Account Tracking

  • Persistent numeric User ID: https://x.com/i/user/<id> works even after renames.
  • Snowflake timestamps: (id >> 22) + 1288834974657 = Unix ms.
  • Wayback CDX, Nitter, memory.lol for historical data. See social-media.md.

Tumblr Investigation

  • Blog check: curl -sI for x-tumblr-user header. Avatar at /avatar/512. See social-media.md.

Username OSINT

Image Analysis & Reverse Image Search

  • Google Lens (crop to region of interest), Google Images, TinEye, Yandex (faces). Check corners for visual stego. Twitter strips EXIF. See geolocation-and-media.md.
  • Cropped region search: Isolate distinctive elements (shop signs, building facades) and search via Google Lens for better results than full-scene search. See geolocation-and-media.md.
  • Reflected text: Flip mirrored/reflected text (water, glass) horizontally; search partial text with quoted strings. See geolocation-and-media.md.

Geolocation

  • Railroad signs, infrastructure maps (OpenRailwayMap, OpenInfraMap), process of elimination. See geolocation-and-media.md.
  • Street View panorama matching: Feature extraction + multi-metric image similarity ranking against candidate panoramas. Useful when challenge image is a crop of a Street View photo. See geolocation-and-media.md.
  • Road sign OCR: Extract text from directional signs (town names, route numbers) to pinpoint road corridors. Driving side + sign style + script identify the country. See geolocation-and-media.md.
  • Architecture + brand identification: Post-Soviet concrete = Russia/CIS; named businesses → search locations/branches → cross-reference with coastline/terrain. See geolocation-and-media.md.
  • Music-themed landmark geolocation: Multiple images of music-related landmarks worldwide; each yields a piano key number encoding one flag character. Identify all locations first, then decode the key sequence. See geolocation-and-media.md.

MGRS Coordinates

Google Plus Codes

  • Format XXXX+XXX (chars: 23456789CFGHJMPQRVWX). Drop a pin on Google Maps → Plus Code appears in details. Free, no API key needed. See geolocation-and-media.md.

Metadata Extraction

exiftool image.jpg           # EXIF data
pdfinfo document.pdf         # PDF metadata
mediainfo video.mp4          # Video metadata

Google Dorking

site:example.com filetype:pdf
intitle:"index of" password

Image TBS filters: Append &tbs=itp:face to Google Image URLs to filter for faces only (strips logos/banners). See web-and-dns.md.

Google Docs/Sheets

  • Try /export?format=csv, /pub, /gviz/tq?tqx=out:csv, /htmlview. See web-and-dns.md.

DNS Reconnaissance

dig -t txt subdomain.ctf.domain.com
dig axfr @ns.domain.com domain.com  # Zone transfer

Always check TXT, CNAME, MX for CTF domains. See web-and-dns.md.

Tor Relay Lookups

  • https://metrics.torproject.org/rs.html#simple/<FINGERPRINT> -- check family, sort by "first seen". See web-and-dns.md.

GitHub Repository Analysis

  • Check issue comments, PR reviews, commit messages, wiki edits via gh api. See web-and-dns.md.

Telegram Bot Investigation

  • Find bot references in browser history, interact via /start, answer verification questions. See web-and-dns.md.

FEC Political Donation Research

  • FEC.gov for committee receipts; 501(c)(4) orgs obscure original funders. See web-and-dns.md.

IP Geolocation

curl "http://ip-api.com/json/103.150.68.150"

See geolocation-and-media.md.

Unicode Homoglyph Steganography

Pattern: Visually-identical Unicode characters from different blocks (Cyrillic, Greek, Math) encode binary data in social media posts. ASCII = 0, homoglyph = 1. Group bits into bytes for flag. See social-media.md.

BlueSky Public API

No auth needed. Endpoints: public.api.bsky.app/xrpc/app.bsky.feed.searchPosts?q=..., app.bsky.actor.searchActors, app.bsky.feed.getAuthorFeed. Check all replies to official posts. See social-media.md.

Fake Service Banner Detection

Pattern: Port appears open on a standard service port (22/SSH, 80/HTTP) but runs a fake service. nmap -sV or nc host port reveals the flag in the banner. Never trust port numbers alone -- always fingerprint the service. See web-and-dns.md.

Shodan SSH Fingerprint Lookup

Search Shodan by SSH host key fingerprint to identify servers: shodan search "fingerprint:AA:BB:CC:...". See web-and-dns.md.

Gaming Platform OSINT

Lookup usernames across gaming platforms (Steam, Xbox, PSN, MMOs) for character profiles, activity, and linked accounts. See social-media.md.

Resources

  • Shodan - Internet-connected devices
  • Censys - Certificate and host search
  • VirusTotal - File/URL reputation
  • WHOIS - Domain registration
  • Wayback Machine - Historical snapshots

Frequently asked questions about CTF OSINT

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