Vulnerability · Published Nov 4, 2026 · Assigned by Checkmarx
CVE-2026-121373Symfony: HtmlSanitizer MetaRefreshAttributeSanitizer Matches Only a Narrow Subset of the Browser Refresh Grammar (Incomplete Fix for CVE-2026-48761)
Medium 5.3
In plain English
A medium-severity open redirect in symfony from sensiolabs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 42% of all known vulnerabilities).
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu:26.04:LTS | symfony | no fix listed | UBUNTU-CVE-2026-121373 |
| Ubuntu:26.10 | symfony | no fix listed | UBUNTU-CVE-2026-121373 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| sensiolabs | symfony | 6.1.0 – before 6.4.507.0.0 – before 7.4.238.0.0 – before 8.1.11 |
Weakness: CWE-186, CWE-601 · Vector: 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