CVE-2023-23623: Electronjs Electron XSS Vulnerability

CVE-2023-23623 Overview

CVE-2023-23623 is a critical security vulnerability in the Electron framework that allows Content-Security-Policy (CSP) bypass in renderer processes with disabled sandbox. Electron is a widely-used framework for building cross-platform desktop applications using JavaScript, HTML, and CSS. When a CSP is configured to disallow eval() by setting a script-src directive without the unsafe-eval option, this policy is not properly enforced in renderers where sandbox: false is set in the webPreferences object.

This security flaw allows attackers to execute methods like eval() and new Function() despite explicit CSP restrictions, significantly expanding the attack surface for applications built on affected Electron versions.

Critical Impact

Applications using Electron versions 22.x and 23.x with disabled sandbox are vulnerable to CSP bypass, enabling arbitrary JavaScript code execution via eval() and new Function() methods that should be blocked by security policies.

Affected Products

• Electron 22.0.0 (including all beta releases: beta1 through beta8)
• Electron 23.0.0-alpha1
• All Electron applications with sandbox: false in webPreferences

Discovery Timeline

• 2023-09-06 - CVE CVE-2023-23623 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-23623

Vulnerability Analysis

This vulnerability stems from improper enforcement of Content-Security-Policy directives in Electron's renderer processes when sandbox mode is disabled. The CSP mechanism is designed to prevent execution of inline scripts and dynamic code evaluation through eval() and similar functions. However, when a renderer is initialized with sandbox: false in the webPreferences configuration, the CSP restrictions are not properly applied, creating a security gap.

The flaw is classified under CWE-670 (Always-Incorrect Control Flow Implementation), indicating that the control flow logic responsible for enforcing CSP rules fails to execute correctly under specific conditions—namely when the sandbox is disabled.

Root Cause

The root cause lies in Electron's handling of Content-Security-Policy enforcement across different renderer contexts. The CSP enforcement mechanism appears to be tightly coupled with the sandbox feature, causing the security policy to be bypassed when sandbox is disabled. This design flaw means that even when developers explicitly configure a restrictive CSP without unsafe-eval, the policy is ineffective in non-sandboxed renderers.

Attack Vector

The vulnerability is exploitable through network-based attack vectors. An attacker who can inject or control content loaded in an Electron application's renderer process can leverage this bypass to execute arbitrary JavaScript code using eval() or new Function() constructors. This is particularly dangerous in scenarios where:

• The application loads remote content or third-party resources
• An attacker achieves a cross-site scripting (XSS) position within the application
• The application processes untrusted input that reaches the renderer

The vulnerability allows attackers to bypass developer-intended security restrictions, potentially leading to remote code execution, data exfiltration, or further exploitation of the underlying system depending on the application's privileges and Node.js integration settings.

Detection Methods for CVE-2023-23623

Indicators of Compromise

• Unexpected eval() or new Function() calls in application logs or monitoring systems
• JavaScript execution patterns that should be blocked by configured CSP rules
• Anomalous script behavior in Electron renderer processes
• Evidence of dynamic code generation or execution in non-sandboxed renderer contexts

Detection Strategies

• Audit Electron application configurations for sandbox: false settings in webPreferences
• Implement runtime monitoring for eval() and new Function() invocations
• Review CSP violation reports for unexpected allowances or missing violation logs
• Monitor for signs of code injection or XSS exploitation in Electron applications

Monitoring Recommendations

• Enable CSP violation reporting to detect attempted policy bypasses
• Implement application-level logging for dynamic code execution methods
• Deploy endpoint detection and response (EDR) solutions like SentinelOne Singularity to detect anomalous JavaScript execution patterns
• Regularly audit renderer process configurations across all Electron applications

How to Mitigate CVE-2023-23623

Immediate Actions Required

• Upgrade Electron to version 22.0.1 or later for the 22.x release line
• Upgrade Electron to version 23.0.0-alpha.2 or later for the 23.x release line
• Enable sandbox mode by setting sandbox: true in the webPreferences object for all renderers
• Review and audit all Electron application configurations for insecure renderer settings

Patch Information

The Electron team has addressed this vulnerability in the following versions:

• Version 22.0.1 - Contains the fix for the 22.x major release line
• Version 23.0.0-alpha.2 - Contains the fix for the 23.x major release line

Organizations should upgrade to the latest stable version of Electron as recommended by the maintainers. For detailed information, refer to the GitHub Security Advisory GHSA-gxh7-wv9q-fwfr.

Workarounds

• Enable sandbox: true on all renderers if upgrading is not immediately possible
• Implement additional input validation and sanitization to reduce XSS attack surface
• Use contextIsolation and disable nodeIntegration to limit potential exploitation impact
• Review and strengthen CSP configurations as a defense-in-depth measure

// Secure webPreferences configuration example
const mainWindow = new BrowserWindow({
  webPreferences: {
    sandbox: true,  // Enable sandbox to enforce CSP properly
    contextIsolation: true,  // Isolate preload scripts from renderer
    nodeIntegration: false,  // Disable Node.js in renderer
    webSecurity: true  // Ensure web security features are enabled
  }
});