CVE-2019-18978 is a medium-severity (CVSS 5.3) Path Traversal vulnerability in rack-cors. A fix is available for rack-cors — see the affected versions and patch details below.
The rack-cors rubygem may allow directory traveral
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
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
An issue was discovered in the rack-cors (aka Rack CORS Middleware) gem before 1.0.4 for Ruby. It allows ../ directory traversal to access private resources because resource matching does not ensure that pathnames are in a canonical format.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | rack-cors | all versions | 1.0.4bundle update rack-cors --conservative |
Affected Products
ubuntu linuxcanonicaldebian linuxdebianrack-corsrack-cors_projectDetection & 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 1.0.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2019-18978 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.
Frequently Asked Questions
Is CVE-2019-18978 in your dependencies?
Find it across RubyGems, including transitive dependencies.