Symfony: HtmlSanitizer UrlAttributeSanitizer Misses URL Attributes
Description
Symfony\Component\HtmlSanitizer\Visitor\AttributeSanitizer\UrlAttributeSanitizer::getSupportedAttributes() enumerates the attribute names whose values are scrubbed through UrlSanitizer::sanitize() (scheme and host allow-lists, javascript: rejection, BiDi check, etc.). The list is ['src', 'href', 'lowsrc', 'background', 'ping', 'action', 'formaction', 'poster', 'cite']. Other URL-bearing attributes are absent: <object data=…>, <applet codebase=…>, <applet archive=…> and <object archive=…>, <iframe longdesc=…> and <img longdesc=…>. When an integrator opts these elements/attributes in via allowElement('object', ['data']), allowElement('applet', ['codebase']), etc., or via allowAttribute(), no URL sanitization runs: data="javascript:alert(1)" and similar payloads ship through unchanged into the output, enabling stored XSS.
<meta http-equiv="refresh" content="0; url=…"> is the same class of bug routed differently: the URL is embedded inside a multi-field content attribute that the per-attribute sanitizer cannot detect from the attribute name alone. Integrators who enable <meta> with the content attribute (e.g. via allowStaticElements()) see content="0; url=javascript:alert(1)" pass through, producing a refresh-driven navigation to a javascript: URL.
Default configurations are not affected: <object>, <applet> and <iframe> are not in W3CReference::BODY_ELEMENTS and <meta> requires an explicit opt-in to <head> context. The vulnerability surface is integrators who explicitly allow any of those elements together with the listed URL-bearing attributes.
Resolution
UrlAttributeSanitizer now also routes data, codebase, archive and longdesc through UrlSanitizer::sanitize(). A new MetaRefreshAttributeSanitizer registered as a default attribute sanitizer detects the <delay>; url=<url> syntax inside <meta content>, sanitizes the embedded URL, and drops the attribute if the URL is rejected; non-refresh meta content values are passed through unchanged.
The patches for this issue are available here for branch 6.4 (and forward-ported to 7.4, 8.0 and 8.1).
Credits
Symfony would like to thank Scott Arciszewski (Trail of Bits) for reporting the issue and Nicolas Grekas for providing the fix.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Composer package | symfony/html-sanitizer | >= 6.1.0, < 6.4.41, >= 7.0.0, < 7.4.13, >= 8.0.0, < 8.0.13 | 6.4.41, 7.4.13, 8.0.13 |
| Composer package | symfony/symfony | >= 6.1.0, < 6.4.41, >= 7.0.0, < 7.4.13, >= 8.0.0, < 8.0.13 | 6.4.41, 7.4.13, 8.0.13 |
References
- https://github.com/symfony/symfony/security/advisories/GHSA-x5qj-865h-mgvm
- https://github.com/symfony/symfony/commit/069a70f9f26e61e9de3b7f9a864a86ed24b36bd0
- https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/html-sanitizer/CVE-2026-48761.yaml
- https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/symfony/CVE-2026-48761.yaml
- https://github.com/symfony/symfony
- https://symfony.com/cve-2026-48761
- CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N- Weakness (CWE)
CWE-1023, CWE-79- Platform
- Composer
- Package
symfony/html-sanitizer, symfony/symfony- Disclosed
- 15.06.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-x5qj-865h-mgvm - CC BY 4.0
Vulnerability history: symfony/html-sanitizer
All published vulnerabilities of this package (Composer package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 5
- First → latest
- 05.2026 06.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Medium 4
- Low 1
Disclosures per year
- 2026: 5
-
Symfony: HtmlSanitizer UrlAttributeSanitizer Misses URL Attributes this entry
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