CVE-2017-11173 is a high-severity (CVSS 8.8) vulnerability in rack-cors. A fix is available for rack-cors — see the affected versions and patch details below.
Missing Regex anchor in Rack-Cors allows malicious third party site to perform CORS request
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-2017-11173 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 378,567 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
rack-corsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
Missing anchor in generated regex for rack-cors before 0.4.1 allows a malicious third-party site to perform CORS requests. If the configuration were intended to allow only the trusted example.com domain name and not the malicious example.net domain name, then example.com.example.net (as well as example.com-example.net) would be inadvertently allowed.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | rack-cors | all versions | 0.4.1bundle update rack-cors --conservative |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for rack-cors, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update rack-cors to 0.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2017-11173 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 CVE-2017-11173 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2017-11173. 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-2017-11173 in your dependencies?
O3 Security finds CVE-2017-11173 across RubyGems dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.