CVE-2019-18889
CRITICALCVE-2019-18889 is a critical-severity (CVSS 9.8) Code Injection vulnerability in symfony/cache. EPSS puts its 30-day exploitation probability at 33.2% (98th percentile). O3 Security confirms whether CVE-2019-18889 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Symfony Unsafe Cache Serialization Could Enable RCE
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.
How urgent is this, really
CVE-2019-18889 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 363,908 CVEs with a current EPSS score, this one falls in the 10–50% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
symfony/cache🐘symfony/cache🐘symfony/cache🐘symfony/symfony🐘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
An issue was discovered in Symfony 3.4.0 through 3.4.34, 4.2.0 through 4.2.11, and 4.3.0 through 4.3.7. Serializing certain cache adapter interfaces could result in remote code injection. This is related to symfony/cache.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | symfony/cache | ≥ 3.1.0&&< 3.4.35 | 3.4.35 |
| 🐘Packagist | symfony/cache | ≥ 4.0.0&&< 4.2.12 | 4.2.12 |
| 🐘Packagist | symfony/cache | ≥ 4.3.0&&< 4.3.8 | 4.3.8 |
| 🐘Packagist | symfony/symfony | ≥ 3.1.0&&< 3.4.35 | 3.4.35 |
| 🐘Packagist | symfony/symfony | ≥ 4.0.0&&< 4.2.12 | 4.2.12 |
| 🐘Packagist | symfony/symfony | ≥ 4.3.0&&< 4.3.8 | 4.3.8 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/cache. 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/cache to 3.4.35 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2019-18889 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-2019-18889 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-2019-18889. 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-2019-18889 in your dependencies?
O3 detects CVE-2019-18889 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.