EUVD-2026-5591: Critical Sandbox Escape Vulnerability Analysis

Executive Summary

Vulnerability Classification: Critical Sandbox Escape CVSS Score: 10.0 (Critical) Affected Software: SandboxJS < 0.8.29 Status: Patched in version 0.8.29

This vulnerability represents a complete sandbox escape mechanism in SandboxJS, a JavaScript sandboxing library, allowing attackers to execute arbitrary code outside the intended security boundary with no authentication or user interaction required.

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1. Vulnerability Assessment and Severity Evaluation

Severity Analysis

The CVSS 3.1 score of 10.0 is justified by the following vector components:

• Attack Vector (AV:N): Network-based exploitation possible
• Attack Complexity (AC:L): Low complexity; straightforward exploitation
• Privileges Required (PR:N): No privileges needed
• User Interaction (UI:N): No user interaction required
• Scope (S:C): Scope change - breaks out of security boundary
• Confidentiality (C:H): Complete information disclosure
• Integrity (I:H): Complete system compromise possible
• Availability (A:H): Complete denial of service possible

Technical Assessment

This is a sandbox escape vulnerability of the highest severity. The core issue stems from improper isolation of return values from sandboxed functions, allowing attackers to obtain references to the host JavaScript environment's Function constructor. This fundamentally defeats the purpose of the sandbox, which is to provide a secure execution environment for untrusted code.

Critical Factors:

• Complete bypass of security controls
• Trivial exploitation requiring minimal technical sophistication
• No defensive mechanisms can prevent exploitation in vulnerable versions
• Affects the fundamental security model of the library

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2. Potential Attack Vectors and Exploitation Methods

Exploitation Chain

The vulnerability exploits a flaw in how SandboxJS handles return values from functions. The attack chain proceeds as follows:

// Conceptual exploitation flow:

// Step 1: Use Object.values() or Object.entries() on a sandboxed object
// These methods return Arrays containing references to functions

// Step 2: The returned Array contains unwrapped references to the host environment
let hostArray = Object.values(someObject);

// Step 3: Use Array.prototype.at() to access array elements
// This provides access to host Function objects

// Step 4: Access the Function constructor from the host environment
let HostFunction = hostArray.constructor;

// Step 5: Execute arbitrary code outside the sandbox
HostFunction('return process')().mainModule.require('child_process').exec('malicious_command');

Attack Scenarios

Scenario 1: Web Application with User-Provided Code Execution

Context: A web platform allowing users to run custom JavaScript code in a "safe" environment

Attack Flow:

1. Attacker submits malicious code through the platform's code execution interface
2. Code exploits the sandbox escape to access Node.js APIs
3. Attacker gains file system access, can read environment variables, or execute system commands
4. Sensitive data (API keys, database credentials) is exfiltrated

Impact: Complete server compromise, data breach, lateral movement

Scenario 2: Plugin/Extension Systems

Context: Applications using SandboxJS to isolate third-party plugins

Attack Flow:

1. Malicious plugin is installed or compromised plugin is updated
2. Plugin code uses the vulnerability to escape sandbox restrictions
3. Access to main application context and resources
4. Privilege escalation to application-level permissions

Impact: Application compromise, data manipulation, persistent backdoor installation

Scenario 3: Educational/Testing Platforms

Context: Online coding platforms, interview systems, or educational tools

Attack Flow:

1. Attacker uses the platform's code execution feature
2. Escapes sandbox to access underlying infrastructure
3. Pivots to attack other users' sessions or platform infrastructure
4. Potential for cryptomining, botnet enrollment, or data theft

Impact: Infrastructure compromise, multi-tenant security breach

Scenario 4: Serverless/Edge Computing

Context: Edge computing platforms using SandboxJS for function isolation

Attack Flow:

1. Attacker deploys or compromises a function
2. Escapes sandbox to access shared resources
3. Attacks adjacent functions or platform infrastructure
4. Establishes persistence or exfiltrates data

Impact: Cloud infrastructure compromise, cross-tenant attacks

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3. Affected Systems and Software Versions

Directly Affected

• SandboxJS versions: All versions prior to 0.8.29
• Vendor: nyariv (GitHub: nyariv/SandboxJS)
• Package Ecosystem: npm (Node.js package manager)

Potentially Affected Downstream Systems

Any application or service utilizing SandboxJS for security isolation, including:

1. Code Execution Platforms

   • Online IDEs and coding environments
   • Code interview and assessment platforms
   • Educational programming platforms

2. Plugin/Extension Frameworks

   • Applications with user-extensibility features
   • Workflow automation tools
   • Low-code/no-code platforms

3. Content Management Systems

   • CMS platforms with custom scripting capabilities
   • Template engines with JavaScript execution

4. API Gateways and Middleware

   • Systems allowing custom request/response transformation
   • API testing and mocking tools

5. Serverless Platforms

   • Function-as-a-Service (FaaS) implementations
   • Edge computing platforms

Detection Methods

Organizations can identify affected systems using:

# Check npm dependencies
npm list sandboxjs

# Check for vulnerable versions in package.json
grep -r "sandboxjs.*0\.[0-7]\." package.json
grep -r "sandboxjs.*0\.8\.\([0-9]\|1[0-9]\|2[0-8]\)" package.json

# Scan with npm audit
npm audit

# Check yarn dependencies
yarn why sandboxjs

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4. Recommended Mitigation Strategies

Immediate Actions (Priority 1 - Within 24 Hours)

1. Update to Patched Version

# Update SandboxJS to version 0.8.29 or later
npm update sandboxjs@latest

# Or explicitly install the patched version
npm install sandboxjs@0.8.29

# Verify the update
npm list sandboxjs

2. Emergency Workarounds (if immediate patching is not possible)

• Disable affected functionality: Temporarily disable any features that execute user-provided code
• Network isolation: Restrict network access for systems running vulnerable versions
• Enhanced monitoring: Implement aggressive logging and monitoring for suspicious activity

3. Incident Response Assessment

• Review logs for potential exploitation attempts
• Look for unusual process executions, network connections, or file access patterns
• Check for indicators of compromise (IOCs):
  • Unexpected child processes
  • Unusual network connections from sandboxed environments
  • File system modifications outside expected patterns
  • Privilege escalation attempts

Short-Term Actions (Priority 2 - Within 1 Week)

1. Comprehensive Dependency Audit

# Generate complete dependency tree
npm list --all > dependency_audit.txt

# Check for transitive dependencies
npm audit --json > audit_report.json

# Use automated scanning tools
npx snyk test

2. Security Architecture Review

• Evaluate the security model of applications using SandboxJS
• Assess whether additional security layers are needed
• Consider defense-in-depth strategies:
  • Operating system-level sandboxing (containers, VMs)
  • Process isolation
  • Principle of least privilege
  • Network segmentation

3. Implement Additional Security Controls

• Resource limits: Implement CPU, memory, and execution time limits
• Network restrictions: Use firewall rules to limit outbound connections
• File system isolation: Use chroot, containers, or VMs for additional isolation
• Monitoring and alerting: Deploy runtime application self-protection (RASP) or similar technologies

Long-Term Actions (Priority 3 - Within 1 Month)

1. Security Testing Program

• Implement regular security testing for sandbox escape vulnerabilities
• Conduct penetration testing focused on isolation boundaries
• Establish bug bounty program for security researchers