CVE-2026-45753 Symfony's HtmlSanitizer UrlAttributeSanitizer Omits action/formaction/poster/cite — `javascript`: URI Survives Sanitization (XSS)
Attackers can inject JavaScript via unsanitized URL attributes in Symfony HTML Sanitizer, leading to XSS when specific attributes are enabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-45753?
CVE-2026-45753 is a low-severity cross-site scripting vulnerability in Sensiolabs Symfony, published on 14 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Symfony is a PHP framework for web and console applications and a set of reusable PHP components. From 6.1.0-BETA1 until 6.4.40, 7.4.12, and 8.0.12, UrlAttributeSanitizer::getSupportedAttributes() omits URL-valued attributes including action, formaction, poster, and cite, so configurations that admit those attributes can leave javascript: URIs unsanitized and enable XSS when the resulting HTML is rendered or a victim submits a form or clicks a button. This issue is fixed in versions 6.4.40, 7.4.12, and 8.0.12.
Which versions are affected by CVE-2026-45753?
12 open source packages ship an affected version, including symfony/html-sanitizer and symfony/symfony. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
symfony/html-sanitizer Packagist | From 6.1.0 | 6.4.40 |
symfony/html-sanitizer Packagist | From 6.1.0 | 6.4.40 |
symfony/html-sanitizer Packagist | From 7.0.0 | 7.4.12 |
symfony/html-sanitizer Packagist | From 7.0.0 | 7.4.12 |
symfony/html-sanitizer Packagist | From 8.0.0 | 8.0.12 |
symfony/html-sanitizer Packagist | From 8.0.0 | 8.0.12 |
6 more packages
symfony/symfony Packagist | From 6.1.0 | 6.4.40 |
symfony/symfony Packagist | From 6.1.0 | 6.4.40 |
symfony/symfony Packagist | From 7.0.0 | 7.4.12 |
symfony/symfony Packagist | From 7.0.0 | 7.4.12 |
symfony/symfony Packagist | From 8.0.0 | 8.0.12 |
symfony/symfony Packagist | From 8.0.0 | 8.0.12 |
Products include Sensiolabs Symfony.
How do I fix CVE-2026-45753?
Upgrade symfony/html-sanitizer to a fixed version for your release line: 6.4.40, 7.4.12 or 8.0.12.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-45753 being exploited?
There is no known exploitation of CVE-2026-45753 in the wild and no public exploit code.
Other vulnerabilities in Sensiolabs Symfony
Sources
Also known as DEBIAN-CVE-2026-45753, GHSA-hhg7-c65m-h7ff, UBUNTU-CVE-2026-45753.