CVE-2026-48761

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.

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.

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.

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.

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.

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.

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.

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.