In Eclipse Theia versions up to and including 0.16.0, in the notification messages there is no HTML escaping, so Javascript code can run.
{
"cwe_ids": [
"CWE-829"
],
"github_reviewed": true,
"github_reviewed_at": "2021-05-07T17:57:37Z",
"nvd_published_at": "2021-03-12T22:15:00Z",
"severity": "MODERATE"
}