CVE-2026-48761: Symfony: HtmlSanitizer UrlAttributeSanitizer Misses URL Attributes on <object>, <applet>, <iframe>, <img> and the URL Inside <meta http-equiv="refresh"> content
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::BODYELEMENTS 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.
Other sources
Symfony is a PHP framework for web and console applications and a set of reusable PHP components. From 6.1.0 until 6.4.41, 7.4.13, and 8.0.13, UrlAttributeSanitizer::getSupportedAttributes() omitted URL-bearing attributes on <object>, <applet>, <iframe>, and <img>, and <meta http-equiv="refresh"> URLs inside content bypassed URL sanitization, allowing explicitly enabled elements or attributes to pass javascript: and similar payloads into sanitized output. This issue is fixed in versions 6.4.41, 7.4.13, and 8.0.13.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
composer/symfony/symfonyto a version that resolves this vulnerability.Fixed in 8.0.13 - Upgrade
Upgrade
composer/symfony/symfonyto a version that resolves this vulnerability.Fixed in 7.4.13 - Upgrade
Upgrade
composer/symfony/symfonyto a version that resolves this vulnerability.Fixed in 6.4.41 - Upgrade
Upgrade
composer/symfony/html-sanitizerto a version that resolves this vulnerability.Fixed in 8.0.13 - Upgrade
Upgrade
composer/symfony/html-sanitizerto a version that resolves this vulnerability.Fixed in 7.4.13 - Upgrade
Upgrade
composer/symfony/html-sanitizerto a version that resolves this vulnerability.Fixed in 6.4.41 - Upgrade
Upgrade
symfony/html-sanitizerto a version that resolves this vulnerability.Fixed in 6.4.41 - Upgrade
Upgrade
symfony/html-sanitizerto a version that resolves this vulnerability.Fixed in 7.4.13 - Upgrade
Upgrade
symfony/html-sanitizerto a version that resolves this vulnerability.Fixed in 8.0.13
Event History
Frequently Asked Questions
What is the severity of CVE-2026-48761?
The severity of CVE-2026-48761 is rated at 55.
What systems are affected by CVE-2026-48761?
CVE-2026-48761 affects the Symfony components, specifically composer/symfony/symfony and composer/symfony/html-sanitizer.
How do I fix CVE-2026-48761?
To fix CVE-2026-48761, update your Symfony components to the latest version that addresses this vulnerability.
What type of vulnerability is CVE-2026-48761?
CVE-2026-48761 is classified as an XSS vulnerability.
Where can I find more information about CVE-2026-48761?
Additional information about CVE-2026-48761 can be found on the official Symfony GitHub repository.