Cloudanix VulnDB

CVE-2026-45753

Medium · 4.6

Symfony's HtmlSanitizer UrlAttributeSanitizer Omits action/formaction/poster/cite — `javascript`: URI Survives Sanitization (XSS)

CVSS

4.6

EPSS

0.3%

Published

May 28, 2026

CISA due date

—

The record

`symfony/html-sanitizer` lets applications sanitise untrusted HTML. `UrlAttributeSanitizer` is the visitor responsible for validating URL-valued attributes and stripping dangerous schemes from them; it runs on every element regardless of configuration. Whether an attribute is *kept* is decided by the element/attribute allow-list; validating the *scheme* of a URL attribute is solely `UrlAttributeSanitizer`'s responsibility. `UrlAttributeSanitizer::getSupportedAttributes()` returned only `['src', 'href', 'lowsrc', 'background', 'ping']`. The HTML URL-valued attributes `action` (`<form>`), `formaction` (`<button>`, `<input type=image>`), `poster` (`<video>`) and `cite` (`<blockquote>`, `<q>`, `<del>`, `<ins>`) were missing from that list, so `DomVisitor` never invoked scheme validation for them. As a result, when a configuration admits one of those attributes, a `javascript:` URI in it survived sanitisation.

Affected packages

Ecosystem Package Introduced Fixed

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