GHSA-mmcv-fvq8-r9x3 is a critical-severity (CVSS 9.8) remote code execution vulnerability in symfony/symfony. A fix is available for symfony/symfony — see the affected versions and patch details below.
Symfony XML decoding attack vector through external entities
Real-World Exposure
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
The XMLEncoder component of Symfony 2.0.x fails to disable external entities when parsing XML. In the Symfony2 framework the XML class may be used to deserialize objects or as part of a client/server API. By using external entities it is possible to include arbitrary files from the file system.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | symfony/symfony | ≥ 2.0.0&&< 2.0.11 | 2.0.11composer require symfony/symfony:^2.0.11 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/symfony, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update symfony/symfony to 2.0.11 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-mmcv-fvq8-r9x3 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-mmcv-fvq8-r9x3 can be triaged on real exposure rather than presence alone.
Tailored to GHSA-mmcv-fvq8-r9x3. 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-mmcv-fvq8-r9x3 in your dependencies?
O3 Security finds GHSA-mmcv-fvq8-r9x3 across Packagist dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.