Answer in brief
CVE-2026-121373 records a Medium severity (CVSS 5.3) vulnerability in Symfony: HtmlSanitizer MetaRefreshAttributeSanitizer Matches Only a Narrow Subset of the Browser Refresh Grammar (Incomplete Fix for CVE-2026-48761). The current sources do not mark it as known exploited. The current feed maps sensiolabs/symfony/html-sanitizer (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 5.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps sensiolabs/symfony/html-sanitizer (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| sensiolabs/symfony/html-sanitizergeneric | >=6.1 <6.4.50 || >=7 <7.4.23 || >=8 <8.1.11 | 6.4.50, 7.4.23, 8.1.11 |
Published upstream
Nov 4, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Nov 4, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Nov 4, 2026
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.
Quoted source text, attributed separately from HOL analysis.