CVE-2021-4070
📋 TL;DR
CVE-2021-4070 is an off-by-one error in v2ray-core that can lead to memory corruption and potential remote code execution. This affects all users running v2ray-core versions prior to 4.44.0. Attackers could exploit this vulnerability to compromise v2ray servers and potentially gain control over affected systems.
💻 Affected Systems
- v2fly/v2ray-core
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data exfiltration, and lateral movement within the network.
Likely Case
Denial of service through application crashes or memory corruption, potentially leading to service disruption.
If Mitigated
Limited impact with proper network segmentation and minimal exposure, potentially only causing application instability.
🎯 Exploit Status
The vulnerability is publicly documented with technical details available, making exploitation feasible for skilled attackers.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 4.44.0 and later
Vendor Advisory: https://github.com/v2fly/v2ray-core/commit/c1af2bfd7aa59a4482aa7f6ec4b9208c1d350b5c
Restart Required: Yes
Instructions:
1. Stop v2ray service. 2. Update to v2ray-core version 4.44.0 or later using your package manager or manual installation. 3. Restart v2ray service. 4. Verify the new version is running.
🔧 Temporary Workarounds
Network Segmentation
linuxRestrict network access to v2ray instances using firewall rules to limit exposure.
iptables -A INPUT -p tcp --dport [v2ray_port] -s [trusted_ips] -j ACCEPT
iptables -A INPUT -p tcp --dport [v2ray_port] -j DROP
🧯 If You Can't Patch
- Implement strict network access controls to limit which hosts can connect to v2ray instances
- Monitor v2ray logs for unusual activity and implement intrusion detection systems
🔍 How to Verify
Check if Vulnerable:
Check v2ray version with: v2ray version | grep 'V2Ray'Check Version:
v2ray versionVerify Fix Applied:
Confirm version is 4.44.0 or higher: v2ray version | grep 'V2Ray 4.4[4-9]\|V2Ray [5-9]'📡 Detection & Monitoring
Log Indicators:
- Unexpected v2ray process crashes
- Memory allocation errors in v2ray logs
- Unusual connection patterns to v2ray
Network Indicators:
- Abnormal traffic patterns to v2ray ports
- Connection attempts with malformed packets
SIEM Query:
source="v2ray.log" AND ("panic" OR "segmentation fault" OR "memory corruption")