CVE-2026-45305 in Symfony YAML
Symfony YAML can hang on crafted YAML because of slow regex backtracking.
Quick answer
Symfony YAML should be reviewed and updated if it matches the affected versions. The recommended fix is to apply the vendor-supported patched version or the mitigation steps below, then retest the public website with Fixnx.
Who is affected
Affected versions
- symfony/yaml <5.4.52, >=6.0.0 <6.4.40, >=7.0.0 <7.4.12, >=8.0.0 <8.0.12
Fixed versions
- symfony/yaml 5.4.52, 6.4.40, 7.4.12, or 8.0.12
How to fix it
Update Symfony YAML. The old package can let unsafe input, requests, or tokens pass checks they should not pass.
- Update symfony/yaml to symfony/yaml 5.4.52, 6.4.40, 7.4.12, or 8.0.12 with Composer.
- Run the app test suite.
- Clear Symfony cache and redeploy.
- Check logs after release.
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Verify the fix
- Run composer show symfony/yaml and confirm the fixed version is installed.
- Retest the affected XML, YAML, login, token, cache, or email path.
Related categories
Trusted references
FAQ
What is affected by CVE-2026-45305?
Symfony YAML versions listed as affected should be reviewed: symfony/yaml <5.4.52, >=6.0.0 <6.4.40, >=7.0.0 <7.4.12, >=8.0.0 <8.0.12.
What should I fix first?
Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.
How do I confirm the fix worked?
Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.
How are Fixnx security risk categories chosen?
Fixnx keeps one canonical risk page and assigns only broad, relevant categories such as ecosystem, technology area, or vulnerability class.