CVE-2019-5420
📋 TL;DR
This CVE allows remote attackers to guess the automatically generated development mode secret token in vulnerable Rails versions, which can be combined with other Rails internals to achieve remote code execution. It affects Rails applications running in development mode with versions below the patched releases. Organizations using Rails for development or staging environments are particularly vulnerable.
💻 Affected Systems
- Ruby on Rails
📦 What is this software?
Fedora by Fedoraproject
Rails by Rubyonrails
Rails by Rubyonrails
Rails by Rubyonrails
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with attacker gaining remote code execution, potentially leading to data theft, lateral movement, and complete application control.
Likely Case
Remote code execution in development environments, allowing attackers to execute arbitrary commands, access sensitive data, and pivot to other systems.
If Mitigated
Limited impact if development environments are properly isolated and not internet-facing, with attackers unable to reach vulnerable systems.
🎯 Exploit Status
Exploit code is publicly available and requires no authentication. Attackers can guess the development mode secret token to achieve RCE.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Rails 5.2.2.1, 6.0.0.beta3, or later
Vendor Advisory: https://weblog.rubyonrails.org/2019/3/13/Rails-4-2-5-1-5-1-6-2-have-been-released/
Restart Required: Yes
Instructions:
1. Update Rails gem to version 5.2.2.1 or later for Rails 5.x, or 6.0.0.beta3 or later for Rails 6.x. 2. Run 'bundle update rails' in your application directory. 3. Restart the Rails server. 4. Verify the update with 'rails --version'.
🔧 Temporary Workarounds
Disable development mode on internet-facing systems
allEnsure Rails applications are not running in development mode on internet-facing servers.
export RAILS_ENV=production
rails server -e production
Set explicit secret_key_base
allManually configure secret_key_base instead of using auto-generated development token.
export SECRET_KEY_BASE=your_secure_random_key_here
🧯 If You Can't Patch
- Isolate development environments from production networks and internet access
- Implement network segmentation and firewall rules to restrict access to development servers
🔍 How to Verify
Check if Vulnerable:
Check Rails version and environment: 1. Run 'rails --version' to check version. 2. Check if RAILS_ENV is set to 'development'. 3. Verify if secret_key_base is auto-generated in development mode.Check Version:
rails --versionVerify Fix Applied:
1. Run 'rails --version' to confirm version is 5.2.2.1+ or 6.0.0.beta3+. 2. Verify secret_key_base is properly configured and not using development mode defaults.📡 Detection & Monitoring
Log Indicators:
- Unusual requests to development endpoints
- Suspicious command execution in logs
- Failed secret token guessing attempts
Network Indicators:
- Traffic to development server ports from unexpected sources
- Exploit payload patterns in HTTP requests
SIEM Query:
source="rails.log" AND ("development" OR "secret_key_base") AND ("error" OR "exception")🔗 References
- http://packetstormsecurity.com/files/152704/Ruby-On-Rails-DoubleTap-Development-Mode-secret_key_base-Remote-Code-Execution.html
- https://groups.google.com/forum/#%21topic/rubyonrails-security/IsQKvDqZdKw
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/Y43636TH4D6T46IC6N2RQVJTRFJAAYGA/
- https://weblog.rubyonrails.org/2019/3/13/Rails-4-2-5-1-5-1-6-2-have-been-released/
- https://www.exploit-db.com/exploits/46785/
- http://packetstormsecurity.com/files/152704/Ruby-On-Rails-DoubleTap-Development-Mode-secret_key_base-Remote-Code-Execution.html
- https://groups.google.com/forum/#%21topic/rubyonrails-security/IsQKvDqZdKw
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/Y43636TH4D6T46IC6N2RQVJTRFJAAYGA/
- https://weblog.rubyonrails.org/2019/3/13/Rails-4-2-5-1-5-1-6-2-have-been-released/
- https://www.exploit-db.com/exploits/46785/
