Server-Side Request Forgery (SSRF) vulnerability & Its Fixation

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Server-Side Request Forgery (SSRF) occurs when an attacker manipulates a server to send HTTP requests to unintended internal or external systems.

Attacker can pass internal URLs like http://localhost:8080/admin, potentially exposing internal services.

Impact of SSRF

  • Access to internal-only resources (e.g., cloud metadata, admin panels).
  • Port scanning internal networks.
  • Bypassing firewalls and network segmentation.
  • In severe cases, remote code execution or cloud credential theft (e.g., AWS IAM keys).

Solution to Fix SSRF

To prevent or fix SSRF (Server-Side Request Forgery) vulnerabilities, you need to implement strong input validation, network restrictions, and safe request handling. Below is a structured SSRF mitigation checklist and sample solutions based on common environments.

1. Input Validation and Whitelisting

Only allow requests to explicitly defined, trusted domains/IPs.

2. Avoid Direct Use of User Input in HTTP Requests

Block:
  • 127.0.0.1, localhost
  • Private IPs: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16
  • AWS/GCP metadata services: 169.254.169.254

3. Use a Network Firewall / egress filtering

  • Deny the web app from accessing the internal network unless explicitly needed.
  • Example: AWS Security Groups, Docker --network=none.

4. Enforce DNS Rebinding Protections

  • Perform DNS resolution and validate IP against blocklists.
  • Re-validate after redirection (e.g., avoid redirecting to internal IPs).