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fingerprinting-server-software

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Identify the server software, framework, and component versions a target is running from its HTTP response signatures — Server header, X-Powered-By, Via, X-AspNet-Version, X-Runtime, X-Drupal-Cache, X-Generator, Set-Cookie name patterns, error-page artwork, HTTP method behavior signatures. Use when: penetration test reconnaissance phase, post-deploy audit of fingerprintable exposure, or before reporting "no obvious version disclosure" to an auditor. Threshold: any version string in a response header (e.g., Server header with nginx/1.18.0, X-Powered-By with PHP/7.4.21, X-Generator with Drupal 9), or any framework-default Set-Cookie name (PHPSESSID, JSESSIONID, connect.sid, _csrf_token). Trigger with: "fingerprint server", "version disclosure", "tech-stack identification", "what's this site running".

plugins/security/penetration-tester/skills/fingerprinting-server-software/SKILL.md

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Nov 12, 2026
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MIT

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# Fingerprinting Server Software

## Overview

Version disclosure is the cheapest recon an attacker buys. A single
GET request returns the `Server:` header, the `X-Powered-By:` header,
and any framework-default cookies. From those three signals the
attacker derives: web server family + exact version, app-framework +
version, language runtime + version. That maps directly to a CVE
catalog query: every published CVE affecting any of those components,
filtered to ones an unauthenticated attacker can trigger.

The fix is operationally trivial (one line in nginx, one line in
Apache, one line in IIS) but the discipline isn't universal. This
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