wstg-info-02

Test ID

WSTG-INFO-02

Test Name

Fingerprint Web Server

High-Level Description

Web server fingerprinting is the process of identifying the type, version, and configuration of a web server. This information is critical for penetration testers as it helps identify known vulnerabilities associated with specific server versions. Attackers use this information to find and exploit unpatched vulnerabilities. Understanding what web server software is running allows testers to focus their efforts on relevant attack vectors.

What to Check

Information to Identify

• ] Web server software (Apache, nginx, IIS, LiteSpeed, etc.)
• ] Web server version number
• ] Operating system information
• ] Installed modules and extensions
• ] Server configuration details
• ] Backend technologies (PHP, ASP.NET, Java, etc.)
• ] Load balancer or reverse proxy presence
• ] CDN (Content Delivery Network) information
• ] WAF (Web Application Firewall) presence

How to Test

Step 1: HTTP Header Analysis

Examine HTTP response headers to identify server information.

Using curl

bash
# Basic header request
curl -I https://target.com

# Verbose output with headers
curl -v https://target.com 2>&1 | grep -i "server\|x-powered-by\|x-aspnet"

# Follow redirects
curl -ILk https://target.com

Using wget

bash
# Get headers only
wget --server-response --spider https://target.com 2>&1 | grep -i server

Key Headers to Examine

| Header | Information Revealed | | --------------------- | --------------------------------- | | Server | Web server software and version | | X-Powered-By | Backend technology (PHP, ASP.NET) | | X-AspNet-Version | ASP.NET version | | X-AspNetMvc-Version | ASP.NET MVC version | | X-Generator | CMS or framework information | | X-Drupal-Cache | Drupal CMS indicator | | X-Varnish | Varnish cache presence | | Via | Proxy server information | | X-Cache | CDN/Cache information | | CF-Ray | Cloudflare indicator | | X-Amz-Cf-Id | AWS CloudFront indicator |

Step 2: Banner Grabbing

Using Telnet (HTTP)

bash
# Connect to HTTP port
telnet target.com 80

# Send request (type manually)
HEAD / HTTP/1.1
Host: target.com

# Press Enter twice

Using OpenSSL (HTTPS)

bash
# Connect to HTTPS port
openssl s_client -connect target.com:443 -quiet

# Send request (type manually)
HEAD / HTTP/1.1
Host: target.com

# Press Enter twice

Using Netcat

bash
# HTTP
echo -e "HEAD / HTTP/1.1\r\nHost: target.com\r\n\r\n" | nc target.com 80

# With timeout
echo -e "HEAD / HTTP/1.1\r\nHost: target.com\r\n\r\n" | nc -w 5 target.com 80

Step 3: HTTP Header Order Analysis

Different web servers return headers in characteristic orders:

Apache Header Order

Date
Server
Last-Modified
ETag
Accept-Ranges
Content-Length
Connection
Content-Type

nginx Header Order

Server
Date
Content-Type
Content-Length
Connection
Last-Modified
ETag
Accept-Ranges

IIS Header Order

Content-Length
Content-Type
ETag
Last-Modified
Accept-Ranges
Server
X-Powered-By
Date

Step 4: Malformed Request Testing

Send invalid HTTP requests to trigger error pages that may reveal server information.

bash
# Invalid HTTP version
echo -e "GET / INVALIDVERSION/1.1\r\nHost: target.com\r\n\r\n" | nc target.com 80

# Invalid method
echo -e "INVALID / HTTP/1.1\r\nHost: target.com\r\n\r\n" | nc target.com 80

# Long URL
python3 -c "print('GET /' + 'A'*5000 + ' HTTP/1.1\r\nHost: target.com\r\n\r\n')" | nc target.com 80

Error Page Signatures

| Server | Error Page Characteristics | | --------- | ------------------------------------ | | Apache | DOCTYPE HTML 2.0, "Apache" in footer | | nginx | Simple HTML, "nginx" in title/body | | IIS | Detailed error with "Microsoft-IIS" | | LiteSpeed | "LiteSpeed" branding | | lighttpd | XHTML format |

Step 5: Default Page and File Analysis

bash
# Check default pages
curl -s https://target.com/server-status    # Apache
curl -s https://target.com/nginx_status     # nginx
curl -s https://target.com/server-info      # Apache
curl -s https://target.com/phpinfo.php      # PHP info
curl -s https://target.com/web.config       # IIS
curl -s https://target.com/.htaccess        # Apache

# Check favicon hash (can identify technology)
curl -s https://target.com/favicon.ico | md5sum

Step 6: SSL/TLS Certificate Analysis

bash
# Get certificate details
openssl s_client -connect target.com:443 2>/dev/null | openssl x509 -noout -text

# Quick issuer check
echo | openssl s_client -connect target.com:443 2>/dev/null | openssl x509 -noout -issuer -subject

# Check for technology in certificate
openssl s_client -connect target.com:443 2>/dev/null | openssl x509 -noout -text | grep -i "organization\|CN="

Step 7: Response Behavior Analysis

bash
# Check response to different methods
for method in GET POST PUT DELETE OPTIONS TRACE PATCH; do
    echo "=== $method ==="
    curl -X $method -I https://target.com 2>/dev/null | head -5
done

# Check OPTIONS response
curl -X OPTIONS -I https://target.com

Tools

Command-Line Tools

| Tool | Description | Usage | | ------------------ | -------------------------------------- | ---------------------------------------------- | | Nmap | Network scanner with version detection | nmap -sV target.com | | Nikto | Web server scanner | nikto -h target.com | | WhatWeb | Web technology identifier | whatweb target.com | | Wappalyzer CLI | Technology profiler | wappalyzer https://target.com | | httprint | Web server fingerprinting | httprint -h target.com -s signatures.txt | | curl | HTTP client | curl -I target.com | | httpx | Fast HTTP toolkit | echo target.com \| httpx -title -tech-detect |

Online Services

| Service | URL | Purpose | | --------------- | ------------------- | --------------------------- | | Netcraft | netcraft.com | Server identification | | BuiltWith | builtwith.com | Technology profiler | | Wappalyzer | wappalyzer.com | Browser extension | | Shodan | shodan.io | Banner information | | Censys | censys.io | Certificate and banner data | | SecurityHeaders | securityheaders.com | Header analysis |

Browser Extensions

• Wappalyzer
• BuiltWith Technology Profiler
• Retire.js (for JavaScript libraries)

Example Commands/Payloads

Nmap Commands

bash
# Basic version detection
nmap -sV -p 80,443 target.com

# Aggressive version detection
nmap -sV --version-intensity 5 -p 80,443 target.com

# HTTP enumeration scripts
nmap -sV --script=http-server-header -p 80,443 target.com
nmap --script=http-headers -p 80,443 target.com
nmap --script=http-enum -p 80,443 target.com

# Full HTTP reconnaissance
nmap -sV --script="http-*" -p 80,443 target.com

Nikto Commands

bash
# Basic scan
nikto -h https://target.com

# Specify port
nikto -h target.com -p 443 -ssl

# Output to file
nikto -h https://target.com -o report.html -Format html

# Scan with authentication
nikto -h https://target.com -id admin:password

# Tuning options (specific tests)
nikto -h https://target.com -Tuning 1234

WhatWeb Commands

bash
# Basic scan
whatweb target.com

# Aggressive scan
whatweb -a 3 target.com

# Verbose output
whatweb -v target.com

# JSON output
whatweb --log-json=output.json target.com

# Multiple targets
whatweb -i targets.txt

httpx Commands

bash
# Technology detection
echo "target.com" | httpx -tech-detect

# Full probe
echo "target.com" | httpx -title -tech-detect -status-code -web-server

# Multiple targets
cat targets.txt | httpx -tech-detect -o results.txt

Custom Scripts

Python Banner Grabber

python
#!/usr/bin/env python3
import socket
import ssl

def grab_banner(host, port=80, use_ssl=False):
    request = f"HEAD / HTTP/1.1\r\nHost: {host}\r\n\r\n"

    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.settimeout(10)

    if use_ssl:
        context = ssl.create_default_context()
        sock = context.wrap_socket(sock, server_hostname=host)

    sock.connect((host, port))
    sock.send(request.encode())
    response = sock.recv(4096).decode()
    sock.close()

    return response

# Usage
print(grab_banner("target.com", 443, use_ssl=True))

Bash One-Liner for Multiple Targets

bash
# Scan multiple targets for server headers
while read target; do
    echo "=== $target ==="
    curl -sI "https://$target" 2>/dev/null | grep -i "^server:"
done < targets.txt

Remediation Guide

1. Suppress Server Headers

Apache

apache
# In httpd.conf or apache2.conf
ServerTokens Prod
ServerSignature Off

# Using mod_headers
<IfModule mod_headers.c>
    Header unset Server
    Header always unset X-Powered-By
</IfModule>

nginx

nginx
# In nginx.conf
server_tokens off;

# Using headers-more module
more_clear_headers Server;

IIS

xml
<!-- In web.config -->
<system.webServer>
    <httpProtocol>
        <customHeaders>
            <remove name="X-Powered-By" />
            <remove name="Server" />
        </customHeaders>
    </httpProtocol>
    <security>
        <requestFiltering removeServerHeader="true" />
    </security>
</system.webServer>

2. Custom Error Pages

Configure custom error pages that don't reveal server information:

Apache

apache
ErrorDocument 400 /errors/400.html
ErrorDocument 401 /errors/401.html
ErrorDocument 403 /errors/403.html
ErrorDocument 404 /errors/404.html
ErrorDocument 500 /errors/500.html

nginx

nginx
error_page 400 401 403 404 500 502 503 504 /error.html;
location = /error.html {
    internal;
}

3. Use Reverse Proxy

Deploy a hardened reverse proxy (nginx, HAProxy) in front of application servers to mask backend server information.

4. Keep Software Updated

• Regularly apply security patches
• Subscribe to vendor security advisories
• Use automated patch management

5. Remove Default Pages

• Delete default welcome pages
• Remove server info pages (phpinfo, server-status)
• Disable directory listing

Risk Assessment

CVSS Score

Base Score: 5.3 (Medium)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

| Metric | Value | Description | | ------------------- | --------- | ---------------------------- | | Attack Vector | Network | Accessible via internet | | Attack Complexity | Low | Simple techniques required | | Privileges Required | None | No authentication needed | | User Interaction | None | No user interaction required | | Scope | Unchanged | Impact scope unchanged | | Confidentiality | Low | Server version disclosure | | Integrity | None | No integrity impact | | Availability | None | No availability impact |

> Note: While fingerprinting itself is low severity, it enables further attacks. If an outdated vulnerable version is detected, the combined risk increases significantly.

Severity Levels

| Finding | Severity | Description | | ----------------------------- | -------- | ------------------------------- | | Server header visible | Info | General information | | Exact version disclosed | Low | Version number exposed | | Outdated version detected | Medium | Known vulnerabilities may exist | | Critically vulnerable version | High | Active exploits available | | Default pages exposed | Medium | Sensitive configuration visible |

CWE Categories

| CWE ID | Title | Description | | ----------- | ---------------------------------------------------------- | ----------------------------- | | CWE-200 | Exposure of Sensitive Information to an Unauthorized Actor | Server version disclosure | | CWE-16 | Configuration | Improper server configuration | | CWE-693 | Protection Mechanism Failure | Missing security hardening |

References

OWASP References

• OWASP WSTG - Fingerprint Web Server

Tools Documentation

• Nmap Documentation
• Nikto Documentation
• WhatWeb

Additional Resources

• HTTP Headers - MDN
• Apache Security Tips
• nginx Security Controls

Checklist

[ ] HTTP response headers analyzed (curl/wget)
[ ] Banner grabbing performed (telnet/openssl/netcat)
[ ] Server header order analyzed
[ ] Malformed request testing completed
[ ] Default pages checked
[ ] Error pages analyzed
[ ] SSL/TLS certificate examined
[ ] Nmap version detection performed
[ ] Nikto scan completed
[ ] WhatWeb/Wappalyzer analysis done
[ ] Online services checked (Netcraft, BuiltWith)
[ ] CDN/WAF presence identified
[ ] Findings documented
[ ] Risk assessment completed