EUVD-2026-5592: Critical Sandbox Escape Vulnerability Analysis

Executive Summary

EUVD-2026-5592 represents a critical severity sandbox escape vulnerability in SandboxJS, a JavaScript sandboxing library. With a CVSS 3.1 base score of 10.0 (Critical), this vulnerability enables complete sandbox escape through prototype pollution, allowing attackers to execute arbitrary code and compromise the host environment. The vulnerability affects all versions prior to 0.8.29.

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1. Vulnerability Assessment and Severity Evaluation

Severity Classification

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

CVSS Metrics Breakdown

Metric	Value	Interpretation
Attack Vector (AV)	Network (N)	Exploitable remotely without physical access
Attack Complexity (AC)	Low (L)	No specialized conditions required for exploitation
Privileges Required (PR)	None (N)	No authentication or privileges needed
User Interaction (UI)	None (N)	Fully automated exploitation possible
Scope (S)	Changed (C)	Impact extends beyond the vulnerable component
Confidentiality (C)	High (H)	Complete information disclosure possible
Integrity (I)	High (H)	Complete data modification possible
Availability (A)	High (H)	Complete denial of service possible

Severity Justification

The maximum CVSS score is warranted due to:

1. Complete Sandbox Escape: The vulnerability fundamentally breaks the security boundary that SandboxJS is designed to enforce
2. Prototype Pollution: Enables persistent contamination of the JavaScript runtime environment
3. Cross-Sandbox Impact: Compromised state persists across multiple sandbox instances
4. No Prerequisites: Exploitation requires no authentication, user interaction, or complex conditions
5. Remote Exploitation: Can be triggered through network-accessible applications using the vulnerable library

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2. Potential Attack Vectors and Exploitation Methods

Technical Vulnerability Mechanism

The vulnerability exploits a fundamental flaw in SandboxJS's property access control mechanism:

1. hasOwnProperty Shadowing: Attackers can override the hasOwnProperty method on sandbox objects
2. Whitelist Bypass: This shadowing disables prototype whitelist enforcement in the property-access path
3. Direct Prototype Access: With enforcement disabled, attackers gain direct access to __proto__ and other blocked prototype properties
4. Prototype Pollution: Attackers can modify Object.prototype, affecting all JavaScript objects in the host environment

Exploitation Sequence

// Conceptual exploitation flow (simplified)

// Step 1: Shadow hasOwnProperty on sandbox object
sandboxObject.hasOwnProperty = function() { return false; };

// Step 2: Access blocked prototype properties
sandboxObject.__proto__.maliciousProperty = maliciousFunction;

// Step 3: Pollute Object.prototype
Object.prototype.isAdmin = true;
Object.prototype.executeCommand = function(cmd) { /* malicious code */ };

// Step 4: Impact persists across all objects and sandboxes

Attack Scenarios

Scenario 1: Server-Side JavaScript Execution

• Target: Node.js applications using SandboxJS to execute untrusted code
• Impact: Remote Code Execution (RCE) on the server
• Method: Submit malicious JavaScript through user input, API endpoints, or plugin systems

Scenario 2: Multi-Tenant Environments

• Target: SaaS platforms allowing custom JavaScript execution
• Impact: Cross-tenant data access and privilege escalation
• Method: Pollute shared prototype to affect other tenants' sandbox instances

Scenario 3: Browser-Based Sandboxing

• Target: Web applications using SandboxJS for client-side code isolation
• Impact: Cross-site scripting (XSS) escalation, session hijacking
• Method: Inject malicious code through user-controlled content

Scenario 4: Plugin/Extension Systems

• Target: Applications with plugin architectures using SandboxJS
• Impact: Plugin escape leading to host application compromise
• Method: Malicious plugin exploits sandbox to access host resources

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3. Affected Systems and Software Versions

Directly Affected Software

• Product: SandboxJS
• Vendor: nyariv (GitHub: nyariv/SandboxJS)
• Vulnerable Versions: All versions < 0.8.29
• Fixed Version: 0.8.29 and later

Potentially Affected Ecosystems

Server-Side Environments

• Node.js applications implementing:
  • User-provided code execution (code playgrounds, REPLs)
  • Template engines with JavaScript evaluation
  • Serverless function platforms
  • Workflow automation systems
  • API gateway scripting layers

Client-Side Environments

• Browser-based applications implementing:
  • In-browser code editors and IDEs
  • Educational coding platforms
  • Low-code/no-code development tools
  • Browser extension sandboxing

Specialized Use Cases

• IoT and Edge Computing: Devices running JavaScript-based automation
• Game Development: Modding systems using JavaScript sandboxing
• Content Management Systems: Custom scripting capabilities
• Business Process Management: Rule engines with JavaScript evaluation

Dependency Chain Risks

Organizations should audit:

• Direct dependencies on SandboxJS
• Transitive dependencies through other packages
• Custom forks or modified versions
• Embedded or bundled instances

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4. Recommended Mitigation Strategies

Immediate Actions (Priority 1 - Critical)

1. Emergency Patching

# Update to fixed version immediately
npm update sandboxjs@0.8.29
# or
yarn upgrade sandboxjs@0.8.29

Timeline: Within 24-48 hours of advisory publication

2. Dependency Audit

# Identify vulnerable instances
npm audit
npm ls sandboxjs

# Check for transitive dependencies
npm ls --all | grep sandboxjs

3. Temporary Workarounds (if immediate patching is impossible)

• Disable untrusted code execution features temporarily
• Implement additional input validation before sandbox entry
• Deploy Web Application Firewall (WAF) rules to detect exploitation attempts
• Isolate affected systems from network access where feasible

Short-Term Mitigations (Priority 2 - High)

4. Runtime Monitoring

Implement detection for exploitation attempts:

// Monitor for hasOwnProperty manipulation
const originalHasOwnProperty = Object.prototype.hasOwnProperty;
Object.defineProperty(Object.prototype, 'hasOwnProperty', {
  get: function() {
    // Log potential exploitation attempt
    console.warn('hasOwnProperty access detected');
    return originalHasOwnProperty;
  },
  configurable: false
});

5. Enhanced Logging

• Enable comprehensive logging of sandbox operations
• Monitor for prototype pollution indicators
• Track unusual property access patterns
• Implement alerting for suspicious activities

6. Network Segmentation

• Isolate systems running vulnerable SandboxJS versions
• Restrict network access to sandbox execution environments
• Implement strict egress filtering

Long-Term Strategic Measures (Priority 3 - Medium)

7. Architecture Review

• Evaluate sandbox necessity: Determine if sandboxing is essential for business requirements
• Consider alternatives: Assess other sandboxing solutions (vm2, isolated-vm, WebAssembly sandboxing)
• Implement defense-in-depth: Don't rely solely on JavaScript-based sandboxing

8. Security Hardening

// Implement additional prototype protection
Object.freeze(Object.prototype);
Object.freeze(Array.prototype);
Object.freeze(Function.prototype);

// Use Content Security Policy (CSP) for browser environments
// Content-Security-Policy: script-src 'self