CVE-2026-121373
Symfony: HtmlSanitizer MetaRefreshAttributeSanitizer Matches Only a Narrow Subset of the Browser Refresh Grammar (Incomplete Fix for CVE-2026-48761)
The 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.
Fixes and workarounds
Fix
The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.
Source: CNA: CheckmarxAffected products and versions
| Product | Versions | Authority |
|---|---|---|
| symfony sensiolabs symfony/html-sanitizer
https://packagist.org/packages/symfony/html-sanitizer |
≥ 6.1; < 6.4.50 (affected, git) ≥ 7; < 7.4.23 (affected, git) ≥ 8; < 8.1.11 (affected, git) Other versions: unaffected |
CNA: Checkmarx |
Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.
CVSS assessments
| Version / score | Vector | Authority |
|---|---|---|
| 4.0 / 5.3 medium |
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 | CNA: Checkmarx |
Exploit evidence
No exploit evidence in collected sources. This is not proof of no exploitation.
References
- https://github.com/symfony/symfony/security/advisories/GHSA-wm2w-4mgj-vw33CNA: Checkmarx · third-party-advisory
- https://github.com/symfony/symfony/commit/2d4c4fe36200858b91132a95076fff3d9de89d26CNA: Checkmarx · patch
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