Summary
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.
Impact
Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
symfony/html-sanitizer to 6.4.41 or later; symfony/html-sanitizer to 7.4.13 or later; symfony/html-sanitizer to 8.0.13 or later; symfony/symfony to 6.4.41 or later; symfony/symfony to 7.4.13 or later; symfony/symfony to 8.0.13 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-48761? CVE-2026-48761 is a medium-severity cross-site scripting (XSS) vulnerability in symfony/html-sanitizer (composer), affecting versions >= 6.1.0, < 6.4.41. It is fixed in 6.4.41, 7.4.13, 8.0.13. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- Which packages are affected by CVE-2026-48761?
symfony/html-sanitizer(composer) (versions >= 6.1.0, < 6.4.41)symfony/symfony(composer) (versions >= 6.1.0, < 6.4.41)
- Is there a fix for CVE-2026-48761? Yes. CVE-2026-48761 is fixed in 6.4.41, 7.4.13, 8.0.13. Upgrade to this version or later.
- Is CVE-2026-48761 exploitable, and should I be worried? Whether CVE-2026-48761 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-48761 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-48761?
- Upgrade
symfony/html-sanitizerto 6.4.41 or later - Upgrade
symfony/html-sanitizerto 7.4.13 or later - Upgrade
symfony/html-sanitizerto 8.0.13 or later - Upgrade
symfony/symfonyto 6.4.41 or later - Upgrade
symfony/symfonyto 7.4.13 or later - Upgrade
symfony/symfonyto 8.0.13 or later
- Upgrade