CVE-2025-27793

Workarounds

• Use vega with expression interpreter
• Upgrade to a newer Vega version (5.32.0)

POC Summary

Calling replace with a RegExp-like pattern calls RegExp.prototype[@@replace], which can then call an attacker-controlled exec function.

POC Details

Consider the function call replace('foo', {__proto__: /h/.constructor.prototype, global: false}). Since pattern has RegExp.prototype[@@replace], pattern.exec('foo') winds up being called.

The resulting malicious call looks like this:

replace(<string argument>, {__proto__: /h/.constructor.prototype, exec: <function>, global: false})

Since functions cannot be returned from this, an attacker that wishes to escalate to XSS must abuse event.view to gain access to eval.

Reproduction steps

{"$schema":"https://vega.github.io/schema/vega/v5.json","signals":[{"name":"a","on":[{"events":"body:mousemove{99999}","update":"replace('alert(1)',{__proto__:/h/.constructor.prototype,exec:event.view.eval,global:false})"}]}]}

Users running Vega/Vega-lite JSON definitions could run unexpected JavaScript code when drawing graphs, unless the library is used with the vega-interpreter.

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.

Kodem intelligence

1. What is CVE-2025-27793? CVE-2025-27793 is a medium-severity cross-site scripting (XSS) vulnerability in vega (npm), affecting versions < 5.32.0. It is fixed in 5.32.0, 5.17.0. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. Which packages are affected by CVE-2025-27793?
   • vega (npm) (versions < 5.32.0)
   • vega-functions (npm) (versions < 5.17.0)
3. Is there a fix for CVE-2025-27793? Yes. CVE-2025-27793 is fixed in 5.32.0, 5.17.0. Upgrade to this version or later.
4. Is CVE-2025-27793 exploitable, and should I be worried? Whether CVE-2025-27793 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
5. What actually determines whether CVE-2025-27793 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.
6. How do I fix CVE-2025-27793?
   • Upgrade vega to 5.32.0 or later
   • Upgrade vega-functions to 5.17.0 or later