{"id":"GHSA-hhg7-c65m-h7ff","summary":"Symfony's HtmlSanitizer UrlAttributeSanitizer Omits action/formaction/poster/cite — `javascript`: URI Survives Sanitization (XSS)","details":"### 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` (`\u003cform\u003e`), `formaction` (`\u003cbutton\u003e`, `\u003cinput type=image\u003e`), `poster` (`\u003cvideo\u003e`) and `cite` (`\u003cblockquote\u003e`, `\u003cq\u003e`, `\u003cdel\u003e`, `\u003cins\u003e`) 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: `\u003cform\u003e` 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* `\u003cform\u003e` + `action`: `allowElement('form', '*')`, `allowElement('form', ['action', …])`, `allowElement('form')-\u003eallowAttribute('action', 'form')`, or the `allowStaticElements()` preset (whose docblock already warns the output \"may still contain other dangerous behaviors\");\n* `\u003cbutton\u003e` / `\u003cinput type=image\u003e` + `formaction`: `allowElement(…, '*')`, `allowAttribute('formaction', …)`, or `allowStaticElements()`;\n* `\u003cblockquote\u003e` / `\u003cq\u003e` / `\u003cdel\u003e` / `\u003cins\u003e` + `cite`, or `\u003cvideo\u003e` + `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 `\u003ca href\u003e`, so `javascript:` is rejected and `data:` is dropped too); `poster` is validated against the media schemes (so `data:` images keep working). The behaviour of `\u003ca href\u003e` and `\u003cimg src\u003e` is unchanged.\n\nOne behaviour change to be aware of: a relative `action=\"/submit\"` on an allowed `\u003cform\u003e` is now dropped by default (the same as `\u003ca href\u003e` / `\u003cimg src\u003e` today); `-\u003eallowRelativeLinks()` 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.","aliases":["CVE-2026-45753"],"modified":"2026-09-10T03:51:06.023129963Z","published":"2026-05-28T16:43:27Z","database_specific":{"github_reviewed_at":"2026-05-28T16:43:27Z","nvd_published_at":null,"cwe_ids":["CWE-184","CWE-79"],"severity":"LOW","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/symfony/symfony/security/advisories/GHSA-hhg7-c65m-h7ff"},{"type":"WEB","url":"https://github.com/symfony/symfony/commit/26a598fcfc4f903cc55ff202f642ee621839825e"},{"type":"WEB","url":"https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/html-sanitizer/CVE-2026-45753.yaml"},{"type":"WEB","url":"https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/symfony/CVE-2026-45753.yaml"},{"type":"PACKAGE","url":"https://github.com/symfony/symfony"},{"type":"WEB","url":"https://symfony.com/cve-2026-45753"}],"affected":[{"package":{"name":"symfony/html-sanitizer","ecosystem":"Packagist","purl":"pkg:composer/symfony/html-sanitizer"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.1.0"},{"fixed":"6.4.40"}]}],"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"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-hhg7-c65m-h7ff/GHSA-hhg7-c65m-h7ff.json"}},{"package":{"name":"symfony/html-sanitizer","ecosystem":"Packagist","purl":"pkg:composer/symfony/html-sanitizer"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"7.0.0"},{"fixed":"7.4.12"}]}],"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"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-hhg7-c65m-h7ff/GHSA-hhg7-c65m-h7ff.json"}},{"package":{"name":"symfony/html-sanitizer","ecosystem":"Packagist","purl":"pkg:composer/symfony/html-sanitizer"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"8.0.0"},{"fixed":"8.0.12"}]}],"versions":["v8.0.0","v8.0.7","v8.0.8"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-hhg7-c65m-h7ff/GHSA-hhg7-c65m-h7ff.json"}},{"package":{"name":"symfony/symfony","ecosystem":"Packagist","purl":"pkg:composer/symfony/symfony"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.1.0"},{"fixed":"6.4.40"}]}],"versions":["v6.1.0","v6.1.1","v6.1.10","v6.1.11","v6.1.12","v6.1.2","v6.1.3","v6.1.4","v6.1.5","v6.1.6","v6.1.7","v6.1.8","v6.1.9","v6.2.0","v6.2.0-BETA1","v6.2.0-BETA2","v6.2.0-BETA3","v6.2.0-RC1","v6.2.0-RC2","v6.2.1","v6.2.10","v6.2.11","v6.2.12","v6.2.13","v6.2.14","v6.2.2","v6.2.3","v6.2.4","v6.2.5","v6.2.6","v6.2.7","v6.2.8","v6.2.9","v6.3.0","v6.3.0-BETA1","v6.3.0-BETA2","v6.3.0-BETA3","v6.3.0-RC1","v6.3.0-RC2","v6.3.1","v6.3.10","v6.3.11","v6.3.12","v6.3.2","v6.3.3","v6.3.4","v6.3.5","v6.3.6","v6.3.7","v6.3.8","v6.3.9","v6.4.0","v6.4.0-BETA1","v6.4.0-BETA2","v6.4.0-BETA3","v6.4.0-RC1","v6.4.0-RC2","v6.4.1","v6.4.10","v6.4.11","v6.4.12","v6.4.13","v6.4.14","v6.4.15","v6.4.16","v6.4.17","v6.4.18","v6.4.19","v6.4.2","v6.4.20","v6.4.21","v6.4.22","v6.4.23","v6.4.24","v6.4.25","v6.4.26","v6.4.27","v6.4.28","v6.4.29","v6.4.3","v6.4.30","v6.4.31","v6.4.32","v6.4.33","v6.4.34","v6.4.35","v6.4.36","v6.4.37","v6.4.38","v6.4.39","v6.4.4","v6.4.5","v6.4.6","v6.4.7","v6.4.8","v6.4.9"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-hhg7-c65m-h7ff/GHSA-hhg7-c65m-h7ff.json"}},{"package":{"name":"symfony/symfony","ecosystem":"Packagist","purl":"pkg:composer/symfony/symfony"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"7.0.0"},{"fixed":"7.4.12"}]}],"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"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-hhg7-c65m-h7ff/GHSA-hhg7-c65m-h7ff.json"}},{"package":{"name":"symfony/symfony","ecosystem":"Packagist","purl":"pkg:composer/symfony/symfony"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"8.0.0"},{"fixed":"8.0.12"}]}],"versions":["v8.0.0","v8.0.1","v8.0.10","v8.0.11","v8.0.2","v8.0.3","v8.0.4","v8.0.5","v8.0.6","v8.0.7","v8.0.8","v8.0.9"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-hhg7-c65m-h7ff/GHSA-hhg7-c65m-h7ff.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:U"}]}