XSS in the `altField` option of the Datepicker widget in jquery-ui

Impact

Accepting the value of the altField option of the Datepicker widget from untrusted sources may execute untrusted code. For example, initializing the datepicker in the following way:

$( "#datepicker" ).datepicker( {
	altField: "<img onerror='doEvilThing()' src='/404' />",
} );

will call the doEvilThing function.

Patches

The issue is fixed in jQuery UI 1.13.0. Any string value passed to the altField option is now treated as a CSS selector.

Workarounds

A workaround is to not accept the value of the altField option from untrusted sources.

For more information

If you have any questions or comments about this advisory, search for a relevant issue in the jQuery UI repo. If you don't find an answer, open a new issue.