EUVD-2026-5590: Critical Sandbox Escape Vulnerability in SandboxJS

Executive Summary

Severity: CRITICAL (CVSS 10.0)

EUVD-2026-5590 represents a critical sandbox escape vulnerability in SandboxJS, a JavaScript sandboxing library. The vulnerability allows complete bypass of sandbox protections through prototype pollution of the Map object, enabling arbitrary code execution with full system privileges. This represents a complete failure of the security boundary that SandboxJS is designed to enforce.

---

1. Vulnerability Assessment and Severity Evaluation

Severity Analysis

• CVSS 3.1 Score: 10.0 (Critical)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

CVSS Breakdown:

• Attack Vector (AV:N): Network-based exploitation possible
• Attack Complexity (AC:L): Low complexity; straightforward exploitation
• Privileges Required (PR:N): No authentication or privileges needed
• User Interaction (UI:N): No user interaction required
• Scope (S:C): Scope change - attacker can affect resources beyond the vulnerable component
• Confidentiality (C:H): Complete information disclosure
• Integrity (I:H): Complete system compromise possible
• Availability (A:H): Complete denial of service possible

Risk Assessment:

This vulnerability represents a complete security boundary failure. The sandbox mechanism, designed to isolate and restrict untrusted JavaScript code execution, can be entirely bypassed. This is particularly severe because:

1. Fundamental Design Flaw: The vulnerability stems from incorrect assumptions about JavaScript prototype chain security
2. Zero Prerequisites: Exploitation requires no authentication, special privileges, or user interaction
3. Complete Compromise: Successful exploitation grants full access to the host environment
4. Widespread Impact: Any application relying on SandboxJS for security isolation is vulnerable

---

2. Potential Attack Vectors and Exploitation Methods

Technical Vulnerability Details

Root Cause: SandboxJS incorrectly includes Map in its SAFE_PROTOTYPES list, allowing attackers to access and manipulate Map.prototype.

Exploitation Mechanism:

// Step 1: Access Map.prototype (incorrectly allowed)
const mapProto = Map.prototype;

// Step 2: Overwrite critical methods like 'has'
mapProto.has = function(key) {
    // Malicious code execution
    // Access to parent scope/context
    // Bypass sandbox restrictions
    return this.constructor.constructor('return this')();
};

// Step 3: Trigger the compromised method
// When sandbox internal code uses Map.has(), malicious code executes
// with full privileges outside the sandbox

Attack Vectors:

Vector 1: Direct Code Injection

• Scenario: Web applications accepting user-provided JavaScript for execution in sandbox
• Method: Submit malicious code that overwrites Map.prototype.has
• Impact: Immediate sandbox escape, access to Node.js/browser APIs

Vector 2: Supply Chain Attack

• Scenario: Malicious npm package or dependency includes exploit code
• Method: Exploit executes during package installation or runtime
• Impact: Complete compromise of development/production environments

Vector 3: Plugin/Extension Systems

• Scenario: Applications using SandboxJS to isolate third-party plugins
• Method: Malicious plugin exploits vulnerability to escape isolation
• Impact: Access to application internals, user data, system resources

Vector 4: Server-Side Template Injection (SSTI)

• Scenario: Server-side JavaScript rendering with SandboxJS protection
• Method: Inject prototype pollution payload through template variables
• Impact: Remote code execution on server infrastructure

Vector 5: WebAssembly/JavaScript Hybrid Attacks

• Scenario: Complex applications mixing WASM and sandboxed JS
• Method: Use WASM to prepare memory state, trigger via JS prototype pollution
• Impact: Advanced persistent threats, memory corruption

Proof of Concept (Conceptual):

// Minimal PoC for sandbox escape
(function() {
    // Overwrite Map.prototype.has
    Map.prototype.has = function() {
        // Gain access to Function constructor
        const FunctionConstructor = this.constructor.constructor;
        
        // Execute arbitrary code outside sandbox
        const globalScope = FunctionConstructor('return this')();
        
        // Example: Access file system (Node.js)
        const fs = globalScope.require('fs');
        fs.writeFileSync('/tmp/pwned', 'Sandbox escaped');
        
        return false; // Return expected value to avoid detection
    };
    
    // Trigger the vulnerability when sandbox uses Map internally
})();

---

3. Affected Systems and Software Versions

Directly Affected:

• Product: SandboxJS (nyariv/SandboxJS)
• Vulnerable Versions: All versions < 0.8.29
• Fixed Version: 0.8.29 and later
• CVE Identifier: CVE-2026-25587

Potentially Affected Ecosystems:

Node.js Applications:

• Server-side JavaScript applications using SandboxJS for code isolation
• Serverless functions (AWS Lambda, Azure Functions, Google Cloud Functions)
• Backend API services processing user-submitted code
• Build systems and CI/CD pipelines executing untrusted scripts

Browser-Based Applications:

• Web-based IDEs and code playgrounds (e.g., JSFiddle-like platforms)
• Online learning platforms with interactive coding exercises
• Browser extensions using SandboxJS for content script isolation
• Progressive Web Apps (PWAs) with plugin architectures

Specific Use Cases at Risk:

1. Low-code/No-code Platforms: User-defined business logic execution
2. Content Management Systems: Custom scripting capabilities
3. Game Engines: User-generated content and modding support
4. Analytics Platforms: Custom metric calculation scripts
5. Workflow Automation Tools: User-defined automation scripts
6. Testing Frameworks: Isolated test execution environments

Dependency Chain Impact:

Applications may be vulnerable through transitive dependencies. Organizations should audit:

• Direct dependencies in package.json/package-lock.json
• Nested dependencies using npm ls sandboxjs or yarn why sandboxjs
• Bundled applications that may include vulnerable versions

---

4. Recommended Mitigation Strategies

Immediate Actions (Priority 1 - Within 24 Hours):

1. Version Upgrade

# Update to patched version immediately
npm update sandboxjs@latest
# or
yarn upgrade sandboxjs@latest

# Verify version
npm ls sandboxjs
# Ensure version >= 0.8.29

2. Emergency Workaround (if immediate upgrade impossible):

// Freeze Map.prototype before initializing sandbox
Object.freeze(Map.prototype);
Object.freeze(Set.prototype);
Object.freeze(WeakMap.prototype);
Object.freeze(WeakSet.prototype);

// Initialize SandboxJS after freezing
const Sandbox = require('sandboxjs');

Warning: This workaround may break legitimate functionality and should only be temporary.

3. Disable Affected Features

• Temporarily disable user code execution features
• Implement strict input validation and sanitization
• Add rate limiting to code execution endpoints

Short-Term Mitigations (Priority 2 - Within 1 Week):

1. Defense in Depth

// Implement additional security layers
const vm = require('vm');
const Sandbox = require('sandboxjs');

function executeUserCode(code) {
    // Layer 1: Input validation
    if (!isValidCode(code)) {
        throw new Error('Invalid code');
    }
    
    // Layer 2: Resource limits
    const timeout = 5000; // 5 seconds
    const memoryLimit = 50 * 1024 * 1024; // 50MB
    
    // Layer 3: VM isolation + SandboxJS
    const context = vm.createContext({
        sandbox: new Sandbox({
            timeout: timeout,