CVE-2025-59840: Vega Visualization Grammar RCE Vulnerability

CVE-2025-59840 Overview

CVE-2025-59840 is an arbitrary JavaScript code execution vulnerability affecting the Vega visualization grammar library. Vega is a declarative format for creating, saving, and sharing interactive visualization designs. Applications using Vega prior to version 6.2.0 are at risk of arbitrary JavaScript code execution, even when the "safe mode" expressionInterpreter is enabled. This vulnerability can be exploited when applications attach the vega library and a vega.View instance to the global window object while also allowing user-defined Vega JSON definitions.

Critical Impact

Arbitrary JavaScript code execution bypassing safe mode protections, potentially leading to data theft, session hijacking, or further compromise of web applications and their users.

Affected Products

• Vega versions prior to 6.2.0
• vega-expression versions prior to 6.1.0 (6.x line) and 5.2.1 / 1.2.1 (non-ESM environments)
• vega-interpreter versions prior to 2.2.1 (when using AST evaluator mode)

Discovery Timeline

• 2025-11-13 - CVE CVE-2025-59840 published to NVD
• 2025-11-14 - Last updated in NVD database

Technical Details for CVE-2025-59840

Vulnerability Analysis

This vulnerability represents a Cross-Site Scripting (XSS) variant that allows arbitrary JavaScript code execution within applications using the Vega visualization library. The vulnerability stems from improper handling of user-supplied Vega JSON definitions when combined with specific global scope configurations.

Applications are vulnerable when two conditions are met simultaneously: the application attaches the vega library and a vega.View instance to the global window object, and the application accepts user-defined Vega JSON definitions rather than exclusively using JSON from source code. Notably, this vulnerability bypasses the "safe mode" expressionInterpreter that developers may rely upon for security, creating a false sense of protection.

The attack vector is network-based and requires user interaction, such as loading a malicious visualization definition. The vulnerability primarily impacts confidentiality and integrity, as attackers can execute arbitrary JavaScript in the context of the victim's browser session.

Root Cause

The root cause lies in the exposure of internal Vega objects through global scope attachment. When the vega library and View instances are accessible via the window object, malicious Vega JSON definitions can access these objects and leverage them to execute arbitrary JavaScript code, bypassing the intended security restrictions of the expressionInterpreter safe mode.

Attack Vector

The attack exploits the network-accessible nature of web applications using Vega. An attacker crafts a malicious Vega JSON definition that, when processed by a vulnerable application, leverages the globally exposed vega objects to execute arbitrary JavaScript code. This could occur through:

1. Direct submission of malicious visualization definitions to applications accepting user input
2. Loading attacker-controlled visualization specifications from untrusted sources
3. Manipulation of shared or collaborative visualization projects

The vulnerability does not require authentication and executes in the context of the victim user's session, potentially allowing access to sensitive data, session tokens, or enabling further attacks such as credential theft.

Detection Methods for CVE-2025-59840

Indicators of Compromise

• Unusual or obfuscated expressions within Vega JSON definitions attempting to access global objects
• Unexpected references to window.vega or window.View within visualization specifications
• JavaScript errors or console messages indicating attempted access to restricted objects
• Anomalous network requests originating from visualization rendering contexts

Detection Strategies

• Review application code for patterns that attach vega or vega.View instances to the global window object
• Audit user-submitted Vega JSON definitions for suspicious expressions or code patterns
• Implement Content Security Policy (CSP) headers to detect and block inline script execution attempts
• Monitor browser console logs in staging environments for unexpected global object access

Monitoring Recommendations

• Enable logging for all user-submitted visualization definitions with content inspection
• Implement Web Application Firewall (WAF) rules to detect potentially malicious Vega JSON patterns
• Monitor for client-side JavaScript errors that may indicate exploitation attempts
• Review referrer headers and origins for visualization definition submissions

How to Mitigate CVE-2025-59840

Immediate Actions Required

• Audit applications to identify if vega or vega.View instances are attached to global variables
• Remove global attachments of vega library and View instances from production code
• Validate and sanitize all user-provided Vega JSON definitions before processing
• Implement strict Content Security Policy headers to limit JavaScript execution contexts

Patch Information

Patches are available for all affected Vega components. For applications using the latest Vega line (6.x), upgrade to:

• vega version 6.2.0 or later
• vega-expression version 6.1.0 or later
• vega-interpreter version 2.2.1 or later (if using AST evaluator mode)

For applications using Vega in a non-ESM environment, upgrade to:

• vega-expression version 5.2.1 or 1.2.1 (if using AST evaluator mode)

For detailed information, refer to the GitHub Security Advisory.

Workarounds

• Do not attach vega View instances to global variables in any environment
• Do not attach the vega library to the global window object
• Avoid debugging practices that expose internal objects globally in production or when handling untrusted definitions
• Restrict Vega/Vega-Lite definitions to trusted sources only; do not process user-provided visualization specifications without thorough validation

# Example: Update Vega packages using npm
npm update vega@^6.2.0 vega-expression@^6.1.0 vega-interpreter@^2.2.1

# Verify installed versions
npm list vega vega-expression vega-interpreter