CVE-2011-5331
📋 TL;DR
CVE-2011-5331 is a critical vulnerability in Distributed Ruby (DRuby) 1.8 that allows remote code execution through improper handling of instance_eval. This affects any system running vulnerable DRuby services, particularly those with exposed DRb endpoints. Attackers can exploit this to execute arbitrary code on affected systems.
💻 Affected Systems
- Distributed Ruby (DRuby)
📦 What is this software?
Distributed Ruby by Distributed Ruby Project
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with remote code execution, allowing attackers to install malware, exfiltrate data, or pivot to other systems.
Likely Case
Remote code execution leading to data theft, service disruption, or lateral movement within the network.
If Mitigated
Limited impact if proper network segmentation and access controls prevent external access to DRuby services.
🎯 Exploit Status
Public exploit code exists and demonstrates straightforward remote code execution.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Ruby 1.9.3 or later
Vendor Advisory: https://www.ruby-lang.org/en/news/
Restart Required: Yes
Instructions:
1. Upgrade Ruby to version 1.9.3 or later. 2. Update all Ruby gems and dependencies. 3. Restart all Ruby services and applications.
🔧 Temporary Workarounds
Disable DRuby Services
linuxDisable or block DRuby (DRb) services if not required
# Stop DRuby services
systemctl stop druby
# Block DRuby ports (default 8787)
iptables -A INPUT -p tcp --dport 8787 -j DROP
Network Segmentation
linuxRestrict network access to DRuby services
# Allow only trusted IPs to access DRuby
iptables -A INPUT -p tcp --dport 8787 -s trusted_ip -j ACCEPT
iptables -A INPUT -p tcp --dport 8787 -j DROP
🧯 If You Can't Patch
- Implement strict network access controls to limit DRuby service exposure
- Monitor DRuby service logs for suspicious activity and unauthorized access attempts
🔍 How to Verify
Check if Vulnerable:
Check Ruby version with 'ruby -v' and verify if DRuby services are running on port 8787 or configured portsCheck Version:
ruby -vVerify Fix Applied:
Confirm Ruby version is 1.9.3 or later and test DRuby functionality for proper operation📡 Detection & Monitoring
Log Indicators:
- Unusual DRuby connection attempts
- Suspicious instance_eval calls in application logs
- Unexpected process execution from Ruby services
Network Indicators:
- Traffic to DRuby default port 8787 from untrusted sources
- Unusual payloads in DRb protocol communications
SIEM Query:
source="*ruby*" AND ("instance_eval" OR "DRb" OR port=8787)