CVE-2020-15240 is a critical-severity (CVSS 9.1) Improper Authentication vulnerability in omniauth-auth0. A fix is available for omniauth-auth0 — see the affected versions and patch details below.
Regression in JWT Signature Validation
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2020-15240 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
omniauth-auth0Real-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
Overview
Versions after and including 2.3.0 are improperly validating the JWT token signature when using the JWTValidator.verify method. Improper validation of the JWT token signature when not using the default Authorization Code Flow can allow an attacker to bypass authentication and authorization.
Am I affected?
You are affected by this vulnerability if all of the following conditions apply:
- You are using
omniauth-auth0. - You are using
JWTValidator.verifymethod directly OR you are not authenticating using the SDK’s default Authorization Code Flow.
How to fix that?
Upgrade to version 2.4.1.
Will this update impact my users?
The fix provided in this version will not affect your users.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | omniauth-auth0 | ≥ 2.3.0&&< 2.4.1 | 2.4.1bundle update omniauth-auth0 --conservative |
Affected Products
omniauth-auth0auth0Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for omniauth-auth0, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update omniauth-auth0 to 2.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-15240 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.
Frequently Asked Questions
Is CVE-2020-15240 in your dependencies?
Find it across RubyGems, including transitive dependencies.