high CVSS 7.5

CVE-2026-45304·PHP vulnerability

Symfony is a PHP framework for web and console applications and a set of reusable PHP components. Prior to 5.4.52, 6.4.40, 7.4.12, and 8.0.12, Symfony\Component\Yaml\Parser resolved YAML collection aliases recursively, allowing a small untrusted YAML input to expand into a multi-gigabyte structure and exhaust memory. This issue is fixed in versions 5.4.52, 6.4.40, 7.4.12, and 8.0.12.

Severity
high
Software
PHP
Fixed in
8.0.12
Published
2026-07-14

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 patch the YAML parser recursive alias resolution flaw that can cause denial-of-service through memory exhaustion. Organizations using Symfony 8.0.0–8.0.11 should prioritize this update, as untrusted YAML input processing could allow attackers to trigger excessive memory consumption on affected servers.

sudo dnf update php

Defensia detects this vulnerability

How to check if you are affected

  1. Check installed PHP version: php -v
  2. Verify Symfony version in your project: composer show symfony/yaml or check vendor/symfony/yaml/composer.json
  3. Search application logs for YAML parsing errors: grep -i 'yaml\|parser' /var/log/apache2/error.log /var/log/nginx/error.log /var/log/php-fpm/error.log
  4. Confirm patch was applied by running php -v and verifying the version is 8.0.12 or later, then test YAML parsing: php -r "require 'vendor/autoload.php'; new Symfony\Component\Yaml\Parser();" without errors

FAQ

What is CVE-2026-45304?

This vulnerability affects Symfony's YAML parser, which recursively resolves collection aliases without depth limits. An attacker can supply a small malicious YAML file containing nested aliases that expands exponentially during parsing, consuming gigabytes of memory and crashing the application.

Is CVE-2026-45304 being actively exploited?

No, this vulnerability is not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog and no public exploit code is available.

What versions of PHP are affected by CVE-2026-45304?

Symfony 8.0.0 through 8.0.11 are vulnerable. Symfony 5.4.52, 6.4.40, 7.4.12, and 8.0.12 and later include the fix.

How do I check if my server is vulnerable to CVE-2026-45304?

Run php -v to check PHP version, then verify Symfony version with composer show symfony/yaml. If Symfony is between 8.0.0 and 8.0.11, the server is vulnerable.

Does Defensia detect CVE-2026-45304?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If PHP is installed on a monitored server, CVE-2026-45304 will appear in your dashboard with remediation steps.

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References

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