medium CVSS 6.1 EPSS 0.30%

CVE-2026-45066·PHP vulnerability

Symfony is a PHP framework for web and console applications and a set of reusable PHP components. From 6.1.0-BETA1 until 6.4.40, 7.4.12, and 8.0.12, HtmlSanitizer URL sanitization can allow off-allowlist URLs through allowLinkHosts() or allowMediaHosts() because UrlSanitizer::parse() follows RFC 3986 while browsers follow WHATWG URL parsing, and because <area href> is checked against the media policy rather than the link policy. This issue is fixed in versions 6.4.40, 7.4.12, and 8.0.12.

Severity
medium
Software
PHP
Fixed in
8.0.12
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at 0.30% — higher than 22% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Affected versions

From: 8.0.0

Until: 8.0.12

Fixed in: 8.0.12

How to fix this CVE

Update PHP and Symfony to versions 8.0.12 or later to resolve a URL sanitization bypass in the HtmlSanitizer component. This vulnerability allows attackers to inject malicious URLs that bypass host allowlists when using allowLinkHosts() or allowMediaHosts() methods. Apply the patch immediately if your application relies on HTML sanitization for user-generated content or third-party data.

sudo dnf update php

Defensia detects this vulnerability

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Implement strict Content Security Policy (CSP) headers with frame-ancestors and default-src directives to limit the impact of injected URLs. Additionally, enforce URL validation on the application layer with a whitelist of known-safe hosts independent of the Symfony HtmlSanitizer until patching is complete.

How to check if you are affected

  1. Step 1: Check PHP version with `php -v` and verify Symfony version in your project's composer.lock file (look for 'symfony/html-sanitizer' entry)
  2. Step 2: Search your codebase for usage of allowLinkHosts() or allowMediaHosts() in HtmlSanitizer configuration files using `grep -r 'allowLinkHosts\|allowMediaHosts' /path/to/project`
  3. Step 3: Review application logs for suspicious URL patterns in sanitized content, particularly URLs with unusual schemes or host segments that should have been blocked
  4. Step 4: Run `composer update symfony/html-sanitizer` and verify the installed version is >= 8.0.12 with `composer show symfony/html-sanitizer`

FAQ

What is CVE-2026-45066?

CVE-2026-45066 is a URL sanitization bypass vulnerability in Symfony's HtmlSanitizer that allows non-allowlisted URLs to pass through host validation filters due to a mismatch between RFC 3986 parsing (used by Symfony) and WHATWG URL parsing (used by browsers). Additionally, <area> tags are incorrectly validated against media policies instead of link policies.

Is CVE-2026-45066 being actively exploited?

No, CVE-2026-45066 is not currently listed on the CISA Known Exploited Vulnerabilities catalog and no public exploits are available. However, it should still be patched promptly as the vulnerability is publicly disclosed.

What versions of PHP are affected by CVE-2026-45066?

CVE-2026-45066 affects Symfony versions 6.1.0-BETA1 through 8.0.11. The fix is available in Symfony 6.4.40, 7.4.12, and 8.0.12 or later. If you use Symfony as a dependency in your PHP application, ensure you're running one of these patched versions.

How do I check if my server is vulnerable to CVE-2026-45066?

Run `composer show symfony/html-sanitizer` to check the version. If the version is below 8.0.12 (or 7.4.12 / 6.4.40 for older branches) and your application uses allowLinkHosts() or allowMediaHosts(), your system is vulnerable.

Does Defensia detect CVE-2026-45066?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If PHP with Symfony is installed on a monitored server, CVE-2026-45066 will appear in your dashboard with remediation steps.

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References

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