GHSA-q3j3-w37x-hq2q
MEDIUMWebcache Poisoning in symfony/http-kernel
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
symfony/http-kernel🐘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
Description
When a Symfony application is running behind a proxy or a load-balancer, you can tell Symfony to look for the X-Forwarded-* HTTP headers. HTTP headers that are not part of the "trusted_headers" allowed list are ignored and protect you from "Cache poisoning" attacks.
In Symfony 5.2, we've added support for the X-Forwarded-Prefix header, but this header was accessible in sub-requests, even if it was not part of the "trusted_headers" allowed list. An attacker could leverage this opportunity to forge requests containing a X-Forwarded-Prefix HTTP header, leading to a web cache poisoning issue.
Resolution
Symfony now ensures that the X-Forwarded-Prefix HTTP header is not forwarded to sub-requests when it is not trusted.
The patch for this issue is available here for branch 5.3.
Credits
We would like to thank Soner Sayakci for reporting the issue and Jérémy Derussé for fixing the issue.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | symfony/http-kernel | ≥ 5.2.0&&< 5.3.12 | 5.3.12 |
| 🐘Packagist | symfony/symfony | ≥ 5.2.0&&< 5.3.12 | 5.3.12 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/http-kernel. 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-kernel to 5.3.12 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-q3j3-w37x-hq2q 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 GHSA-q3j3-w37x-hq2q 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 GHSA-q3j3-w37x-hq2q. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-q3j3-w37x-hq2q in your dependencies?
O3 detects GHSA-q3j3-w37x-hq2q across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.