CVE-2019-7644
📋 TL;DR
CVE-2019-7644 is an information disclosure vulnerability in Auth0's WCF Service JWT library that leaks the expected JWT signature in error messages when signature validation fails. This allows attackers to forge valid JWT tokens and bypass authentication. Applications using vulnerable versions of Auth0-WCF-Service-JWT for JWT validation are affected.
💻 Affected Systems
- Auth0-WCF-Service-JWT
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete authentication bypass allowing attackers to impersonate any user, access sensitive data, and perform unauthorized actions as any identity.
Likely Case
Authentication bypass leading to unauthorized access to protected resources and potential privilege escalation.
If Mitigated
Limited impact if error messages are not exposed to users and proper logging/monitoring is in place.
🎯 Exploit Status
Exploitation requires the attacker to trigger a JWT validation error and capture the error response containing the signature.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.0.4
Vendor Advisory: https://auth0.com/docs/security/bulletins/cve-2019-7644
Restart Required: Yes
Instructions:
1. Update Auth0-WCF-Service-JWT package to version 1.0.4 or later via NuGet. 2. Rebuild and redeploy affected WCF services. 3. Restart application/services.
🔧 Temporary Workarounds
Suppress Error Details
windowsConfigure WCF services to not include detailed error messages in responses to clients.
<serviceDebug includeExceptionDetailInFaults="false" /> in service behavior configuration
Custom Error Handler
windowsImplement custom error handling to sanitize error messages before returning to clients.
Implement IErrorHandler interface in WCF service
🧯 If You Can't Patch
- Implement network-level controls to restrict access to vulnerable services
- Deploy WAF rules to detect and block JWT manipulation attempts
🔍 How to Verify
Check if Vulnerable:
Check project references/NuGet packages for Auth0-WCF-Service-JWT version <1.0.4Check Version:
Get-Package -ProjectName [YourProjectName] | Where-Object {$_.Id -eq 'Auth0-WCF-Service-JWT'} | Select-Object VersionVerify Fix Applied:
Verify Auth0-WCF-Service-JWT package version is 1.0.4 or higher in NuGet package manager📡 Detection & Monitoring
Log Indicators:
- Multiple JWT validation failures from same source
- Error messages containing JWT signature details in logs
Network Indicators:
- Unusual patterns of JWT token submissions with invalid signatures
- Requests triggering specific validation errors
SIEM Query:
source="wcf_logs" AND (message="*signature*" OR message="*JWT*validation*failed*")