CVE-2020-5255
MEDIUMPrevent cache poisoning via a Response Content-Type header in Symfony
Blast Radius
symfony/http-foundation🐘symfony/http-foundation🐘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 4.4.7 and 5.0.7, when a Response does not contain a Content-Type header, affected versions of Symfony can fallback to the format defined in the Accept header of the request, leading to a possible mismatch between the response's content and Content-Type header. When the response is cached, this can prevent the use of the website by other users. This has been patched in versions 4.4.7 and 5.0.7.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | symfony/http-foundation | ≥ 4.4.0&&< 4.4.7 | 4.4.7 |
| 🐘Packagist | symfony/http-foundation | ≥ 5.0.0&&< 5.0.7 | 5.0.7 |
| 🐘Packagist | symfony/symfony | ≥ 4.4.0&&< 4.4.7 | 4.4.7 |
| 🐘Packagist | symfony/symfony | ≥ 5.0.0&&< 5.0.7 | 5.0.7 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/http-foundation. 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/http-foundation to 4.4.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-5255 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-2020-5255 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-2020-5255. 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-2020-5255 in your dependencies?
O3 detects CVE-2020-5255 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.