symfony/ux-autocomplete: XSS via unescaped AJAX response data
Date: 2026-06
Affected: composer/symfony/ux-autocomplete, composer/symfony/ux-autocomplete
Attack vector: xss
Category: vulnerability-disclosure
Severity: Medium
CVE: CVE-2026-49216
CWE: CWE-79

### Description The Stimulus controller shipped with `symfony/ux-autocomplete` renders AJAX response items into the dropdown by interpolating the `text` field directly into HTML template literals (`<div>${item[labelField]}</div>`) inside `_createAutocompleteWithRemoteData()`. The value is parsed as HTML rather than text, so any markup contained in the AJAX response is executed by the browser. When the dropdown values are derived from user-supplied content, an attacker can craft a string that triggers stored XSS in the browser of any other user who later opens a page containing an autocomplete widget backed by the same data. ### Resolution The `option` and `item` renderers used in `_createAutocompleteWithRemoteData()` now use TomSelect's `escape` helper to HTML-escape the value by default. Endpoints that legitimately return HTML (for example, to highlight the search term) can opt back in to the previous behavior by setting `options_as_html: true`. The `AutocompleteChoiceTypeExtension` normalizer that previously forced `options_as_html=false` when `autocomplete_url` was set has been dropped so the opt-in is reachable from the form layer. The patch for this issue is available [here](https://github.com/symfony/ux/commit/842ae54bc74de389299f975f01aafae272cb0019) for branch 2.x (and forward-ported to 3.x). ### Credits Symfony would like to thank Alex Ashkov for reporting the issue and Hugo Alliaume for providing the fix.


Mitigations:

Architectural layers (MAESTRO):