high CVSS 7.5 EPSS 0.80%

CVE-2026-45305·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::cleanup() used regular expressions with overlapping quantifiers for YAML directive, comment, and document marker cleanup, allowing crafted input to make parsing hang for an arbitrarily long time. 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

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at 0.80% — higher than 53% 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.

Read the two together. CVE-2026-45305 scores 7.5 on CVSS, so a successful attack would be serious — but at 0.80%, almost nobody is currently attempting it. That is a different situation from a flaw under mass exploitation, and it is usually the difference between patching on your next maintenance window and patching tonight.

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 that include the patched YAML parser. Symfony versions 5.4.52, 6.4.40, 7.4.12, and 8.0.12 or later contain the fix for the regex-based denial-of-service vulnerability in YAML parsing. Ensure your PHP environment is running the latest stable release to mitigate the risk of resource exhaustion attacks through maliciously crafted YAML input.

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 application: grep -r '"symfony/yaml"' composer.lock | head -1 or check config/packages/*.yaml for framework version
  3. Search web server logs for unusually slow YAML parsing requests: grep -i 'timeout\|hang\|slow' /var/log/apache2/error.log /var/log/nginx/error.log 2>/dev/null
  4. After patching, confirm Symfony version has been updated: composer show symfony/yaml or check your vendor/symfony/yaml/composer.json for version >= 8.0.12

FAQ

What is CVE-2026-45305?

This vulnerability exists in Symfony's YAML parser, which uses inefficient regular expressions with overlapping quantifiers that can cause the parser to hang indefinitely when processing specially crafted YAML input. An attacker can exploit this to cause a denial-of-service condition by exhausting server resources during YAML parsing operations.

Is CVE-2026-45305 being actively exploited?

No, this vulnerability is not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog, and no public exploits are available at this time.

What versions of PHP are affected by CVE-2026-45305?

Symfony versions 8.0.0 through 8.0.11 are vulnerable. Earlier major versions (5.x, 6.x, 7.x) are also affected up to their respective patch levels (5.4.51, 6.4.39, 7.4.11), but version 8.0.12 and later are patched.

How do I check if my server is vulnerable to CVE-2026-45305?

Run `php -v` to check your PHP version, then verify your Symfony YAML component version via `composer show symfony/yaml`. If the version is below 8.0.12 (or below the patched version for your major release), your system is vulnerable.

Does Defensia detect CVE-2026-45305?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If PHP is installed on a monitored server, CVE-2026-45305 will appear in your dashboard with remediation steps.

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References

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