1. Introduction
Server-Side Request Forgery (SSRF) is a critical web security vulnerability where an attacker forces a server to make HTTP requests to an unintended destination. Unlike client-side attacks, SSRF exploits the server’s own privileges and network access, making it capable of bypassing firewalls, reaching internal-only endpoints, and interacting with cloud metadata services.
Why It’s Dangerous in 2025:
- Modern cloud-native apps have microservices with internal APIs.
- SSRF can be chained with cloud metadata access to extract credentials.
- Many WAFs fail against advanced SSRF payload encoding and tunneling.
2. How SSRF Works – The Attack Flow
- Vulnerable Input
- The web application accepts a URL (e.g., image fetcher, PDF converter, webhook tester).
- Server Fetches the Resource
- Instead of the client, the server sends the HTTP request.
- Attacker Controls the Destination
- Malicious URL points to sensitive internal services or cloud metadata endpoints.
- Data Extraction / Internal Pivoting
- Server responds with sensitive internal data, enabling privilege escalation.
3. Real-World SSRF Attack Scenarios
3.1 Internal Network Scanning
Attackers use SSRF to scan internal IP ranges (10.x.x.x, 172.16.x.x, 192.168.x.x) and enumerate services like:
- Internal dashboards
- Jenkins CI/CD admin panels
- Elasticsearch / Kibana
3.2 Cloud Metadata Exploitation
Cloud environments expose metadata services to internal IPs:
- AWS:
http://169.254.169.254/latest/meta-data/ - Azure:
http://169.254.169.254/metadata/ - GCP:
http://metadata.google.internal/
Attackers can extract API keys, IAM roles, and tokens.
3.3 Bypassing IP Restrictions
If an API only allows requests from the server’s IP, SSRF can trick the server into making the request internally.
3.4 Hitting Localhost Services
Attackers can target services bound to 127.0.0.1, like:
- Redis
- Memcached
- Admin UIs without authentication
4. Advanced SSRF Techniques in 2025
| Technique | Description | Example Payload |
|---|---|---|
| DNS Rebinding | Changes DNS resolution mid-request to pivot to internal hosts. | http://attacker-domain.com |
| URL Encoding & Double Encoding | Obfuscates malicious URLs to bypass filters. | %252f%252f169.254.169.254 |
| Open Redirect Abuse | Chaining an open redirect to SSRF payload. | http://trusted.com/redirect?url=http://169.254.169.254 |
| Protocol Smuggling | Using gopher://, ftp://, dict:// to interact with internal services. | gopher://127.0.0.1:6379/_COMMAND |
5. MITRE ATT&CK Mapping
- Initial Access: T1190 – Exploit Public-Facing Application
- Discovery: T1046 – Network Service Scanning
- Credential Access: T1552.005 – Cloud Instance Metadata API
- Lateral Movement: T1021 – Remote Services
6. Detection & Prevention Strategies
A. Input Validation & Allowlisting
- Allow only URLs from trusted domains/IPs.
- Reject IP addresses in private ranges.
B. SSRF-Aware Proxy / WAF Rules
- Detect requests to internal ranges and block them.
- Normalize and decode URLs before validation.
C. Disable Unused Protocols
- Only allow HTTP/HTTPS.
- Block
gopher://,ftp://,file://, etc.
D. Cloud Metadata Protection
- AWS: IMDSv2 only (token-based metadata access).
- GCP/Azure: Restrict metadata endpoints with IAM rules.
E. Network Segmentation
- Separate public-facing servers from internal service networks.
7. Threat Hunting Tips
- Monitor outbound requests from application servers to unusual destinations.
- Log DNS queries to detect access to internal resources.
- Look for multiple requests to cloud metadata endpoints.
8. Case Study – Capital One Breach (2019)
An SSRF vulnerability in a web application firewall allowed attackers to query AWS metadata, retrieve IAM credentials, and exfiltrate millions of credit applications.
Key Takeaway: SSRF + cloud metadata = catastrophic breach potential.
9. CyberDudeBivash Recommendations
- Red Team: Actively test your apps with SSRF payloads during pentests.
- Blue Team: Integrate SSRF detection into your SIEM with specific IOC signatures.
- DevSecOps: Include SSRF testing in CI/CD security gates.
Conclusion
SSRF remains one of the most underestimated yet devastating vulnerabilities in modern cloud environments. With the rise of microservices, internal APIs, and automation pipelines, the attack surface has only grown. Treat every external URL input as untrusted and defend like your cloud keys depend on it — because they do.
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