What’s Vulnerable › Vulnerabilities

CVE-2020-15240: Regression in JWT Signature Validation

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.8% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-10-21 · updated 2026-06-17
• Weakness: CWE-287

Description

omniauth-auth0 (rubygems) versions >= 2.3.0 and < 2.4.1 improperly validate the JWT token signature when using the `jwt_validator.verify` method. Improper validation of the JWT token signature can allow an attacker to bypass authentication and authorization. You are affected by this vulnerability if all of the following conditions apply: 1. You are using `omniauth-auth0`. 2. You are using `JWTValidator.verify` method directly OR you are not authenticating using the SDK’s default Authorization Code Flow. The issue is patched in version 2.4.1.

Affected products

• auth0 omniauth-auth0: from 2.3.0 before 2.4.1 — fixed in 2.4.1

How to fix

Upgrade to a fixed version: auth0 omniauth-auth0 2.4.1. Check the vendor advisory for mitigations.

References

• https://github.com/auth0/omniauth-auth0/commit/fd3a14f4ccdfbc515d1121d6378ff88bf55a7a7a
• https://github.com/auth0/omniauth-auth0/security/advisories/GHSA-58r4-h6v8-jcvm
• https://rubygems.org/gems/omniauth-auth0
• https://github.com/auth0/omniauth-auth0/commit/fd3a14f4ccdfbc515d1121d6378ff88bf55a7a7a
• https://github.com/auth0/omniauth-auth0/security/advisories/GHSA-58r4-h6v8-jcvm
• https://rubygems.org/gems/omniauth-auth0

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