Symfony has an HtmlSanitizer allowLinkHosts() / allowMediaHosts() Bypass via URL-Parser Differentials and Misclassification

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

not scored

EPSS

• CVE-2026-45066: 0.34% estimated exploitation activity in the next 30 days; percentile 27.27 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Description symfony/html-sanitizer lets applications sanitise untrusted HTML. The configuration methods allowLinkHosts([...]) and allowLinkSchemes([...]) are intended to restrict <a href targets to an allowlist of hosts/schemes; allowMediaHosts() / allowMediaSchemes() do the same for <img src etc. Three distinct bypasses allow a content author to smuggle off-allowlist URLs past these checks. First, UrlSanitizer::parse() parses the input following RFC-3986, while browsers follow the WHATWG URL Standard which normalises \ to / before parsing the authority of "special" schemes; so an input like https://evil\@trusted.com/ parses with host trusted.com server-side but navigates to https://evil/ in the browser. Second, WHATWG collapses any run of / after the scheme into //, while RFC-3986 does not; so https:/evil.com/ and https:///evil.com/ parse as host-less (skipping the host allowlist) but resolve to evil.com in the browser. Third, UrlAttributeSanitizer checks 'a' === $element to route…

Published by the source

27 May 2026, 20:13 UTC

Last modified by the source

27 May 2026, 20:13 UTC

Source last checked

26 Oct 2026, 14:40 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-qc95-4862-92fh

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# Patch Next advisory brief: CVE-2026-45066

Advisory: Symfony has an HtmlSanitizer allowLinkHosts() / allowMediaHosts() Bypass via URL-Parser Differentials and Misclassification
IDs: CVE-2026-45066, GHSA-qc95-4862-92fh
Record: https://patchnext.com/advisories/cve-2026-45066 (revision 1, source checked 26 Oct 2026, 14:40 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Unrated
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: symfony/symfony 8.0.12, 7.4.12, 6.4.40; symfony/html-sanitizer 8.0.12, 7.4.12, 6.4.40. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist symfony/symfony: affected >= 6.1.0, < 6.4.40; >= 7.0.0, < 7.4.12; >= 8.0.0, < 8.0.12; fixed in 8.0.12, 7.4.12, 6.4.40
- Packagist symfony/html-sanitizer: affected >= 6.1.0, < 6.4.40; >= 7.0.0, < 7.4.12; >= 8.0.0, < 8.0.12; fixed in 8.0.12, 7.4.12, 6.4.40

## Suggested inspection (read-only)
- Packagist symfony/symfony: check the installed version with your package manager.
- Packagist symfony/html-sanitizer: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on symfony/symfony, symfony/html-sanitizer.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-qc95-4862-92fh (GitHub-reviewed advisory GHSA-qc95-4862-92fh lists affected ranges: Packagist symfony/html-sanitizer >=6.1.0 =7.0.0 =8.0.0 =6.1.0 =7.0.0 =8.0.0 <8.0.12)

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