Agent skill

ctf-osint

Provides open source intelligence techniques for CTF challenges. Use when gathering information from public sources, social media, geolocation, DNS records, username enumeration, reverse image search, Google dorking, Wayback Machine, Tor relays, FEC filings, or identifying unknown data like hashes and coordinates.

View SKILL.md on GitHub Repository
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Install this agent skill to your Project

npx add-skill https://github.com/ljagiello/ctf-skills/tree/main/ctf-osint

Metadata

Additional technical details for this skill

user invocable
false

SKILL.md

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):

bash
pip install shodan Pillow

Linux (apt):

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

macOS (Homebrew):

bash
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

bash
# 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

  • Grid format "4V FH 246 677" -> online converter -> lat/long -> Google Maps. See geolocation-and-media.md.

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

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

Google Dorking

text
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

bash
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

bash
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

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