CVE-2020-5274 is a medium-severity (CVSS 5.4) CWE-209 vulnerability in symfony/error-handler. O3 Security confirms whether CVE-2020-5274 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Exceptions displayed in non-debug configurations in Symfony
Real-World Exposure
symfony/error-handler🐘symfony/error-handler🐘symfony/symfony🐘symfony/symfonyReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
In Symfony before versions 5.0.5 and 4.4.5, some properties of the Exception were not properly escaped when the ErrorHandler rendered it stacktrace. In addition, the stacktrace were displayed even in a non-debug configuration. The ErrorHandler now escape alls properties of the exception, and the stacktrace is only display in debug configuration. This issue is patched in symfony/http-foundation versions 4.4.5 and 5.0.5
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | symfony/error-handler | ≥ 4.4.0&&< 4.4.4 | 4.4.4 |
| 🐘Packagist | symfony/error-handler | ≥ 5.0.0&&< 5.0.4 | 5.0.4 |
| 🐘Packagist | symfony/symfony | ≥ 4.4.0&&< 4.4.4 | 4.4.4 |
| 🐘Packagist | symfony/symfony | ≥ 5.0.0&&< 5.0.4 | 5.0.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/error-handler. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update symfony/error-handler to 4.4.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-5274 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2020-5274 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2020-5274. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2020-5274 in your dependencies?
O3 detects CVE-2020-5274 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.