CVE-2019-18848
📋 TL;DR
This vulnerability in the json-jwt Ruby gem allows improper authentication due to missing element count validation when splitting JWE strings. Attackers could potentially bypass authentication mechanisms or manipulate JWT tokens. Any Ruby application using json-jwt versions before 1.11.0 for JWE processing is affected.
💻 Affected Systems
- json-jwt Ruby gem
📦 What is this software?
Json Jwt by Json Jwt Project
⚠️ Risk & Real-World Impact
Worst Case
Complete authentication bypass allowing unauthorized access to protected resources or systems.
Likely Case
Authentication bypass in specific JWE implementations leading to unauthorized data access.
If Mitigated
Limited impact with proper token validation and additional authentication layers.
🎯 Exploit Status
Exploitation requires understanding of JWE structure and access to JWT tokens.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.11.0
Vendor Advisory: https://github.com/nov/json-jwt/commit/ada16e772906efdd035e3df49cb2ae372f0f948a
Restart Required: Yes
Instructions:
1. Update Gemfile to require 'json-jwt', '>= 1.11.0'
2. Run 'bundle update json-jwt'
3. Restart application server
4. Test JWE functionality
🔧 Temporary Workarounds
Disable JWE functionality
allTemporarily disable JSON Web Encryption features if not required
# Modify application code to avoid JWE usage
🧯 If You Can't Patch
- Implement additional token validation layers
- Monitor authentication logs for suspicious JWE usage patterns
🔍 How to Verify
Check if Vulnerable:
Check Gemfile.lock or run 'bundle show json-jwt' and verify version is < 1.11.0Check Version:
ruby -e "require 'json/jwt'; puts JSON::JWT::VERSION"Verify Fix Applied:
Confirm json-jwt version is >= 1.11.0 and test JWE parsing functionality📡 Detection & Monitoring
Log Indicators:
- Failed JWE parsing attempts
- Unusual authentication patterns with JWT tokens
Network Indicators:
- Unexpected JWE token usage in authentication requests
SIEM Query:
source=application_logs AND (message="*JWE*" OR message="*json-jwt*") AND severity=ERROR🔗 References
- https://github.com/nov/json-jwt/commit/ada16e772906efdd035e3df49cb2ae372f0f948a
- https://github.com/nov/json-jwt/compare/v1.10.2...v1.11.0
- https://lists.debian.org/debian-lts-announce/2020/10/msg00001.html
- https://github.com/nov/json-jwt/commit/ada16e772906efdd035e3df49cb2ae372f0f948a
- https://github.com/nov/json-jwt/compare/v1.10.2...v1.11.0
- https://lists.debian.org/debian-lts-announce/2020/10/msg00001.html
