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The vulnerability CVE-2024-43729 is a DOM-based Cross-Site Scripting (XSS) flaw in the Vega visualization library. It arises from an insecure exposure of the `vega` library and `vega.View` instances to the global `window` object, a practice common in debugging environments like the Vega Editor. Even when using the “safe mode” AST expression interpreter, the architecture allows for the execution of arbitrary JavaScript.
The exploit works by crafting a malicious Vega JSON specification. This payload defines a signal that, upon a `mousemove` event, creates a special object. This object overrides its `toString` method to point to a “gadget” function already present in the global scope, specifically VEGA_DEBUG.vega.CanvasHandler.prototype.on. When this object is used in an expression that triggers an implicit type conversion (like adding it to a number), the overridden `toString` method is called.
This gadget function is then manipulated to achieve code execution. The exploit configures the object’s properties so that `this.eventName` is console.log, `this._handlers` is an object where the key `undefined` contains a malicious string, and `this._handlerIndex` is set to the global `eval` function. When the gadget function executes, it calls this._handlerIndex(this._handlers[this.eventName()]), which effectively becomes eval('alert(origin + " XSS ...")'), leading to DOM XSS.
Platform: Vega
Version: <6.2.0
Vulnerability: DOM XSS
Severity: Critical
date: 2024
Prediction: 2024-10-15
What Undercode Say:
Searching for exposed Vega instances in page source grep -r "VEGA_DEBUG" ./src/ grep -r "vega.View" ./src/
// Check if vega is attached globally
if (window.vega || window.VEGA_DEBUG) {
console.warn("Vega is exposed globally - potential CVE-2024-43729 risk");
}
How Exploit:
An attacker crafts a malicious Vega JSON specification containing a signal with an event listener (e.g., mousemove). The signal’s update expression is a crafted object that overrides `toString` to hijack a global gadget function. When a user interacts with the page (e.g., moves their mouse), the expression is evaluated, triggering the gadget chain that culminates in a call to `eval` with an attacker-controlled string, executing arbitrary JavaScript in the victim’s browser context.
Protection from this CVE
Upgrade to `vega` version 6.2.0 or later, `vega-expression` to 6.1.0 or later, and `vega-interpreter` to 2.2.1 or later. For older Vega lines (5.x), upgrade `vega-expression` to 5.2.1 or 1.2.1. As a workaround, immediately stop attaching the `vega` library and `vega.View` instances to the global `window` object in production environments. Ensure user-provided Vega JSON definitions are treated as untrusted input.
Impact:
This vulnerability leads to full DOM XSS, compromising the confidentiality and integrity of the web application. Attackers can steal authentication tokens, session cookies, and other sensitive data displayed to the user. They can also perform actions on behalf of the victim user, potentially leading to account takeover and unauthorized data manipulation. The attack requires user interaction, such as viewing a malicious visualization.
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Sources:
Reported By: github.com
Extra Source Hub:
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