CVE-2026-121373 · Package
NO FIX YET · SEE WHAT TO DO
The Symfony HtmlSanitizer component fails to sanitize some meta refresh directives, so attacker-supplied URLs pass through unchanged. An attacker can make a sanitized page redirect a visitor to an untrusted site, bypassing the configured link scheme and host allowlists.
first public Nov 4, 2026 · 1 source
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Applications that use the Symfony HtmlSanitizer component to sanitize untrusted HTML and allow meta tags with http-equiv and content, including the allowStaticElements() preset. Applications that do not sanitize user HTML with this component, or that do not allow meta refresh tags, are not exposed.
Not affected if meta-tags-not-allowed, no-user-html
Who cares html-sanitizer, php, symfony
composer show symfony/html-sanitizer and compare it with the fixed ranges below.HtmlSanitizer and allowStaticElements() to see whether meta tags with http-equiv and content are allowed.6.4.50 or later7.4.23 or later8.1.11 or laterThe Symfony HtmlSanitizer component MetaRefreshAttributeSanitizer, introduced to fix CVE-2026-48761, sanitizes the refresh URL of content attributes of meta tags using a regular expression that is too narrow, allowing sanitization to be bypassed, and resulting in potential URL redirection to untrusted sites in Symfony versions 6.1.x prior to 6.4.50, 7.x prior to 7.4.23, and 8.x prior to 8.1.11.
The shared declarative refresh steps in the WHATWG HTML Standard require a broader approach: the separator after the time may be ASCII whitespace alone, with no ; or ,, and the url= keyword is optional. Directives the browser honours, but the regular expression misses are returned unchanged, so the attacker URL skips UrlSanitizer entirely and both allowLinkSchemes and allowLinkHosts are defeated for the refresh navigation.
This is reachable under any configuration that allows meta with http-equiv and content, including the documented allowStaticElements() preset.
This page as .md · .json · in your agent: get_signal("CVE-2026-121373") · 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
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