{"id":"GHSA-hhg7-c65m-h7ff","aliases":["CVE-2026-45753"],"title":"Symfony's HtmlSanitizer UrlAttributeSanitizer Omits action/formaction/poster/cite — `javascript`: URI Survives Sanitization (XSS)","titleSource":"OSV","descriptionSource":"OSV","declaredSeverity":"LOW","description":"### Description\n\n`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.\n\n`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.\n\n### Conditions for exploitation\n\n`allowSafeElements()` is **not** affected: `<form>` and the `formaction` attribute are both flagged unsafe in `W3CReference`, and `allowElement('form')` resets the element's attribute list. Reaching the vulnerable attributes requires a deliberately permissive configuration, for example:\n\n* `<form>` + `action`: `allowElement('form', '*')`, `allowElement('form', ['action', …])`, `allowElement('form')->allowAttribute('action', 'form')`, or the `allowStaticElements()` preset (whose docblock already warns the output \"may still contain other dangerous behaviors\");\n* `<button>` / `<input type=image>` + `formaction`: `allowElement(…, '*')`, `allowAttribute('formaction', …)`, or `allowStaticElements()`;\n* `<blockquote>` / `<q>` / `<del>` / `<ins>` + `cite`, or `<video>` + `poster`: similarly via `'*'`, `allowAttribute()`, or `allowStaticElements()`.\n\nFor the `action` / `formaction` cases the victim must additionally submit the form or click the button.\n\n### Resolution\n\n`UrlAttributeSanitizer` now also handles `action`, `formaction`, `cite` and `poster`. `action` / `formaction` / `cite` are validated against the link schemes (like `<a href>`, so `javascript:` is rejected and `data:` is dropped too); `poster` is validated against the media schemes (so `data:` images keep working). The behaviour of `<a href>` and `<img src>` is unchanged.\n\nOne behaviour change to be aware of: a relative `action=\"/submit\"` on an allowed `<form>` is now dropped by default (the same as `<a href>` / `<img src>` today); `->allowRelativeLinks()` re-enables it.\n\nThe patch for this issue is available [here](https://github.com/symfony/symfony/commit/26a598fcfc4f903cc55ff202f642ee621839825e) for branch 6.4.\n\n### Credits\n\nSymfony would like to thank Himanshu Anand and Rémi Pelloux for reporting the issue and Nicolas Grekas for providing the fix.","severity":"low","score":1.2,"published":"2026-05-28T16:43:27.000Z","modified":"2026-09-10T03:51:06.023Z","withdrawn":false,"knownExploited":false,"affected":[{"ecosystem":"Packagist","name":"symfony/html-sanitizer","sources":[{"name":"OSV · GHSA-hhg7-c65m-h7ff","url":"https://osv.dev/vulnerability/GHSA-hhg7-c65m-h7ff"}],"ranges":[{"events":[{"introduced":"6.1.0"},{"fixed":"6.4.40"}],"type":"ECOSYSTEM"}],"versions":["v6.1.0","v6.1.11","v6.1.9","v6.2.0","v6.2.0-BETA1","v6.2.0-RC1","v6.2.2","v6.2.5","v6.2.7","v6.3.0","v6.3.0-BETA1","v6.3.0-RC1","v6.3.12","v6.3.4","v6.3.7","v6.4.0","v6.4.0-BETA1","v6.4.0-BETA2","v6.4.0-RC1","v6.4.12","v6.4.13","v6.4.17","v6.4.18","v6.4.21","v6.4.24","v6.4.25","v6.4.28","v6.4.3","v6.4.35","v6.4.4","v6.4.7","v6.4.8"],"fixed":["6.4.40"]},{"ecosystem":"Packagist","name":"symfony/html-sanitizer","sources":[{"name":"OSV · GHSA-hhg7-c65m-h7ff","url":"https://osv.dev/vulnerability/GHSA-hhg7-c65m-h7ff"}],"ranges":[{"events":[{"introduced":"7.0.0"},{"fixed":"7.4.12"}],"type":"ECOSYSTEM"}],"versions":["v7.0.0","v7.0.3","v7.0.4","v7.0.7","v7.0.8","v7.1.0","v7.1.0-BETA1","v7.1.0-RC1","v7.1.1","v7.1.10","v7.1.11","v7.1.5","v7.1.6","v7.2.0","v7.2.0-BETA1","v7.2.0-RC1","v7.2.2","v7.2.3","v7.2.6","v7.2.9","v7.3.0","v7.3.0-BETA1","v7.3.0-RC1","v7.3.2","v7.3.3","v7.3.6","v7.4.0","v7.4.0-BETA1","v7.4.0-BETA2","v7.4.0-RC1","v7.4.7","v7.4.8"],"fixed":["7.4.12"]},{"ecosystem":"Packagist","name":"symfony/html-sanitizer","sources":[{"name":"OSV · GHSA-hhg7-c65m-h7ff","url":"https://osv.dev/vulnerability/GHSA-hhg7-c65m-h7ff"}],"ranges":[{"events":[{"introduced":"8.0.0"},{"fixed":"8.0.12"}],"type":"ECOSYSTEM"}],"versions":["v8.0.0","v8.0.7","v8.0.8"],"fixed":["8.0.12"]},{"ecosystem":"Packagist","name":"symfony/symfony","sources":[{"name":"OSV · 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· GHSA-hhg7-c65m-h7ff","url":"https://osv.dev/vulnerability/GHSA-hhg7-c65m-h7ff"}],"ranges":[{"events":[{"introduced":"7.0.0"},{"fixed":"7.4.12"}],"type":"ECOSYSTEM"}],"versions":["v7.0.0","v7.0.1","v7.0.10","v7.0.2","v7.0.3","v7.0.4","v7.0.5","v7.0.6","v7.0.7","v7.0.8","v7.0.9","v7.1.0","v7.1.0-BETA1","v7.1.0-RC1","v7.1.1","v7.1.10","v7.1.11","v7.1.2","v7.1.3","v7.1.4","v7.1.5","v7.1.6","v7.1.7","v7.1.8","v7.1.9","v7.2.0","v7.2.0-BETA1","v7.2.0-BETA2","v7.2.0-RC1","v7.2.1","v7.2.2","v7.2.3","v7.2.4","v7.2.5","v7.2.6","v7.2.7","v7.2.8","v7.2.9","v7.3.0","v7.3.0-BETA1","v7.3.0-BETA2","v7.3.0-RC1","v7.3.1","v7.3.10","v7.3.11","v7.3.2","v7.3.3","v7.3.4","v7.3.5","v7.3.6","v7.3.7","v7.3.8","v7.3.9","v7.4.0","v7.4.0-BETA1","v7.4.0-BETA2","v7.4.0-RC1","v7.4.0-RC2","v7.4.0-RC3","v7.4.1","v7.4.10","v7.4.11","v7.4.2","v7.4.3","v7.4.4","v7.4.5","v7.4.6","v7.4.7","v7.4.8","v7.4.9"],"fixed":["7.4.12"]},{"ecosystem":"Packagist","name":"symfony/symfony","sources":[{"name":"OSV · 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